Method for monitoring the state of microcrystalline change of solid materials

ABSTRACT

A process for monitoring the state of microcrystalline change of solid materials, by observing the frequency of a load-pull oscillator which is RF-coupled to the material under test (preferably by a simple single-ended RF probe). Areas where this technique is of particular interest are in monitoring the curing of shaped aerodynamic composite materials, and in monitoring the curing of concrete and cement compositions.

Continuation of prior application Ser. No. 09/072,822, filed May 5, 1998and which issued as U.S. Pat. No. 5,966,017 on Oct. 12, 1999, which isitself a Continuation of Ser. No. 08/592,716, filed Jan. 26, 1996, whichissued as U.S. Pat. No. 5,748,002 on May 5, 1998 and which itself is aContinuation of PCT/US94/08531, filed Jul. 26, 1994, which is acontinuation of U.S. application Ser. Nos. 08/096,940, 08/096,954,08/096,963, 08/096,964, 08/097,406, 08/097,407, 08/097,408, 08/097,409,08/097,410, 08/097,411, and 08/097,412 all filed Jul. 26, 1993 and allnow abandoned.

BACKGROUND AND SUMMARY OF THE INVENTION

The present invention relates to load-pulled electronic measurement andcharacterization systems.

Extensive work by the present inventors has shown that load-pulledoscillators have important new capabilities for measurement andcharacterization. See U.S. Pat. Nos. 4,862,060, 4,996,490, and5,025,222, and PCT applications WO 91/00997 (published Jan. 24, 1991)and WO 91/08469 (published Jun. 13, 1991); all of which are herebyincorporated by reference. This "load-pull" technology provides aneconomical measurement technique which as improved sensitivities by 100×to 1000× over any prior instrumentation for measurement of microwavephase. This capability makes possible microwave measurements which wereproposed in the 1950s but will now have not been available due to thelack of accurate technology. The ground work which was extensivelyformulated during the early years of microwave spectroscopy may now beutilized to bring about generations of products using this simple butpowerful technique.

The previous work has established many of the basic principles, but hasfocused primarily on monitoring continuous streams of fluids (liquids orgas phase). The inventions disclosed herein provide new concepts for"sampling" the electrical characteristics of a wide variety ofmaterials.

Background: The "Load-Pull" Effect

It is well known to electrical engineers generally (and particularly tomicrowave engineers) that the frequency of an RF oscillator can be"pulled" (i.e. shifted from the frequency of oscillation which would beseen if the oscillator were coupled to an ideal impedance-matched pureresistance), if the oscillator sees an impedance which is different fromthe ideal matched impedance. This, a varying load impedance may causethe oscillator frequency to shift.¹

The present invention sets forth various innovative methods and systemswhich take advantage of this effect. In one class of embodiments, anunbuffered² RF oscillator is loaded by an electromagnetic propagationstructure which is electromagnetically coupled, by proximity, to amaterial for which real-time monitoring is desired. The net compleximpedance³ seen by the oscillator will vary as the characteristics ofthe material in the electromagnetic propagation structure varies. Asthis complex impedance changes, the oscillator frequency will vary.Thus, the frequency variation (which can easily be measured) can reflectchanges in density (due to bonding changes, addition of additionalmolecular chains, etc.), ionic content, dielectric constant, ormicrowave loss characteristics of the medium under study. These changeswill "pull" the resonant frequency of the oscillator system. Changes inthe medium's magnetic permeability will also tend to cause a frequencychange, since the propagation of the RF energy is an electromagneticprocess which is coupled to both electric fields and magnetic fieldswithin the transmission line.

Background: Properties of a Dielectric in a Transmission Line

To help explain the use of the load-pull effect in the disclosedinnovations, the electromagnetics of a dielectric-loaded transmissionline will first be reviewed. If a transmission line is (electrically)loaded with a dielectric material, changes in the composition of thedielectric material may cause electrical changes in the properties ofthe line. In particular, the impedance of the line, and the phasevelocity of wave propagation in the line, may change.

This can be most readily illustrated by first considering propagation ofa plane wave in free space. The propagation of a time-harmonic planewave (of frequency f) in a uniform material will satisfy the reducedwave equation

    (∇.sup.2 +k.sup.2)E=(∇.sup.2 +k.sup.2)H=0,

where

E is the electric field (vector),

H is the magnetic field (vector), and

∇² represents the sum of second partial derivatives along the threespatial axes.

This equation can be solved to define the electric field vector E, atany point r and time t, as

    E(r,t)=E.sub.0 exp[i(k·r-ωt)],

where

k is a wave propagation vector which points in the direction ofpropagation and has a magnitude equal to the wave number k, and

ω=Angular Frequency=2πf.

In a vacuum, the wave number k has a value "k₀ " which is

k₀ =ω/c

=ω(μ₀ ε₀)^(1/2),

where

μ₀ =Magnetic Permeability of vacuum (4π×10⁻⁷ Henrys per meter),

ε₀ =Electric Permittivity of vacuum ((1/36π)×10⁻⁹ Farads per meter), and

c=Speed of light=(μ₀ ε₀)^(-1/2) =2.998×10⁸ meters/second.

However, in a dielectric material, the wave number k is not equal to k₀; instead

k=ω/(c(μ_(r) ε_(r))^(1/2))

=ω(μ₀ μ_(r) ε₀ ε_(r))^(1/2),

where

μ_(r) =Relative Permeability of the material (normalized to thepermeability μ₀ of a vacuum), and

ε_(r) =Relative Permittivity of the material (normalized to thepermittivity ε₀ of a vacuum).

This, if the relative permeability μ_(r) and/or the relativepermittivity ε_(r) vary, the wave number k and the wave propagationvector k will also vary, and this variation will typically affect theload pulled oscillator frequency.⁴

Frequency Hopping in a Load-Pulled Oscillator

In a typical free-running oscillator, the oscillator is defined by aresonant feedback circuit (the "tank" circuit), and can also be pulledslightly by a reactive load,⁵ as noted above. Thus, such an oscillatorcan be broadly tuned by including a varactor in the tank circuit.⁶

As the oscillator's frequency is thus shifted, the phase differencebetween the energy incident on and reflected from the load element(which is preferably a shorted transmission line segment) will change.This phase different will be equal to an exact multiple of 180° at anyfrequency where the electrical length of the transmission line segmentis an exact multiple of λ/4.

As the oscillator frequency passes through such a frequency (i.e. onewhere the transmission line segment's electrical length is equal to amultiple of λ/4), the load's net impedance will change from inductive tocapacitive (or vice versa). As this occurs, the frequency of theoscillator may change abruptly rather than smoothly.⁷ This jump infrequency will be referred to as a frequency "hop".⁸

For a transmission line of length l which contains a dielectric materialof relative dielectric constant ε_(r), the frequency at which one fullwavelength (1λ) exists in the transmission line is equal to c (the speedof light in vacuum, which is 2.995×10⁸ meters/second) divided by thelength of the line in meters and by the square root of the relativedielectric constant of the material:

    Frequency.sub.1λ =c/(lε.sub.r.sup.1/2).

For example, for a one-foot-long line filled with a material having ε₄=1, l=12 inches (=0.3048 meters), and

    Frequency.sub.1λ =(2.99×10.sup.8)/(0.3048×1.0)≈980 MHz.

However, since one wavelength actually contains two excursions frominductive to capacitive reactive impedances, only one-half wavelength isrequired to see one frequency hop of the load pulled oscillator. If thetransmission line is terminated into a short or an open, the resultingeffective length is increased to twice the actual length, since astanding wave is generated (due to the energy incident at the short oropen being reflected back to the input of the transmission line). Inessence, the energy travels down the line, gets reflected, and travelsback to the input. With this taken into account, the first frequencywith a wavelength long enough to cause a frequency "hop" of theoscillator is one fourth the length calculated above, or 245 MHz.

Multiples of this first quarter-wavelength frequency will also cause theimpedance seen at the input to the transmission line to go frominductive to capacitive reactance. The longer the transmission line, thegreater the number of phase transitions that will occur. Longer linelength also multiples the phase changes that are brought about by achange in the dielectric constant. For every one-quarter wavelengthchange in the effective (electrical) length of the line, the compleximpedance seen at the oscillator changes by 180°.

For example, suppose that a given oscillator, coupled into a low lossload with an electrical length of one-quarter wavelength (λ/4), provides50 MHz of load pulling frequency change (total excursion through allphases). If the monitored material changes enough to produce a change ofonly one degree of phase in the electrical length of the load, theoscillator frequency will change by 138.9 kHz. This represents anabsolute resolution of 7.2×10⁻⁶ degrees of phase change for each Hertzof sensitivity.⁹ For every additional quarter wavelength of line length,this sensitivity to phase is multiplied by 1.5. This is due to thechange in phase being an additive function of every additional quarterwave in the measurement section.

In a typical frequency versus voltage plot for a VCO loaded into ashorted transmission line, the height of the "hop" can be measured byholding the VCO tuning voltage constant, while a transmission lineterminated into a short is varied in length¹⁰ to cause a full rotationof the impedance vector seen at the VCO's input port. The resulting dataof frequency versus length of the transmission line will show a jump infrequency (a delta frequency from the bottom of the "hop" to the top ofthe "hop") which coincides with the delta frequency of the "hop" seenwhen the VCO was swept using the tuning voltage.

Thus, if the VCO is swept across a frequency band and the number offrequency "hops" was counted, the number of "hops" reveals the number ofwavelengths in the transmission line.¹¹

This provides a means for determination of the range of dielectricconstant change in a medium even when it rotates the phase vectormultiple times (and therefore, the oscillator frequency returns to thesame value multiple times). If the dielectric constant of the materialin the transmission line is increased, then the above equations showthat the frequency of the first full wavelength is decreased by thesquare root of the dielectric constant. Additionally, this means thatthe number of wavelengths at a fixed frequency increases with increasingdielectric constant. These facts imply that the VCO tuning curve willsee more "hops" as the dielectric constant is increased due to theincreasing fraction or whole wavelengths encountered.

Ideally, the oscillator will not cease oscillations (or break intomultiple frequency oscillation or spectral breakup) into any loadregardless of the load characteristics. However, this is not a strictlynecessary condition for use of the disclosed method and systeminnovations.¹²

Measurement of Substances with a High Microwave Loss Factor

A measure of the dielectric loss of a material is typically given as thedielectric loss tangent (a unitless number) which is defined as thetangent of the imaginary part divided by the real part of the complexdielectric constant. Low loss materials are typically below a losstangent equal to or less than 0.01. When the disclosed systems are usedto measure materials with a high loss factor, the material's absorptionbegins to dominate the load versus frequency effects, but a measurementcapability still exists due to the sensitivity of the load pullingmethod.

Additional Information from Load Pull Measurement

A load-pull system also permits other information to be derived,regarding the substance being monitored.

Difference in Operation Frequency

Additional information can be obtained by returning the VCO, so that thefrequency is forced to change, and making another measurement at a muchhigher frequency. Since materials change properties versus frequency,the amount of frequency change due to load pulling will vary versus thefrequency of operation.

A VCO will typically be designed to cover approximately one octave aboveits turn on frequency. If a VCO would not give enough frequency changeto see the desired range of varying parameters versus operatingfrequency, an additional unbuffered oscillator, which runs at anyfrequency required to obtain appropriate data, may be switched into thecoaxial line.

When two widely spaced frequencies are measured for a medium under studywith a load pulled oscillator, the difference (delta) frequency betweenthose tow measurements will be unique for a given medium. This phenomenawill aid in distinguishing constituents and the progress of mixing orreaction.

Monitoring of Insertion Loss

If the incident power and the reflected power is measured in a systemwhere the final load is a short, the difference in powers will be twicethe insertion of the medium (since two transits occur through the mediumof interest). The insertion loss measurement will aid in determinationof the changing conductivity of the medium or its change in absorptionof the RF energy. This information can be related to the mixing orreaction products to further distinguish unique situations where thefrequency change of the load pulled oscillator is not enough informationor resolution by itself.

Effect of Complex Permeability

The magnetic permeability μ₄ can also be dynamically measured by thedisclosed techniques. Since the velocity varies with (μ_(r)ε_(r))^(-1/2), changes in μ_(r) will change the phase shift through agiven physical length of line, and thus change the frequency of theoscillator.

A sample-containing waveguide, like that of the principally preferredembodiment, will typically have locations where the electric field isstrong but the magnetic field is zero; at such locations onlypermittivity will affect the oscillator load pull frequency. However,there will also commonly be locations in a waveguide where the magneticfields are locally strong and electric field is zero: at theselocations, only the permeability will affect the propagationcharacteristics of the transmission line (and therefore contribute tothe oscillator frequency).

A system can be built to sample (primarily) one of these parameters. Forexample, to sample the permeability, the coaxial transmission line willbe terminated into a short where the medium of interest is located onlyin close proximity to the short. A waveguide structure supports verywell defined electrical and magnetic field functions, and the sample canbe suitably placed in such a structure to measure primarily thepermeability.

Typical compounds and substances do not have varying magneticpermeabilities and therefore, most of the discussion will involve thechanging complex permittivity. However, the effects of changing complexpermeability will create similar changes in the oscillator load pullingcharacteristics. If a substance such a barium titanate in studied, theeffect of the changing permeability must be considered along with thechange in permittivity unless the system is designed specifically tomeasure only one of these.

Coupling the Active Device

An unusual feature of the oscillator configuration used with the presentinvention is the separation of the load of interest from the resonantcircuit proper. The configuration used isolates the two through theactive device. It is the non-linear behavior of the transistor thatprovides the changes in frequency as the load is changed. The loop gainof an oscillator must be unity with an appropriate phase shift to cancelthe negative impedance's imaginary part¹³ around the resonant loop. Theinitial gain of the active device must be greater than unity beforeoscillations can begin in order for the oscillator to be self starting.This extra gain is reduced to unity by the saturation of the activedevice upon establishment of the oscillations. Saturation of a devicenormally also changes the phase shift through the device¹⁴. Thisrequires a change in the operation frequency as the load changes due tothe shift in loop gain and phase by the saturated condition change inthe active device.

Spectral Purity of Oscillator

It has been discovered that, in a system using a free-running oscillatoras described above, spectral purity of the oscillator is an importantconcern. Many microwave oscillators exhibit "spectral breakup," whereinthe spectrum of the oscillator's output actually contains multiplefrequencies. In most microwave oscillators this is not a problem, sincea tuned feedback element will be used to stabilize the gain element,and/or isolation or buffering stages are used to prevent theoscillator's feedback loop from being perturbed by extraneousresonances. However, in a load-pulled system, since such buffer stagesare not used, spectral purity turns out to be quite important. Forexample, a spurious resonance in the feedback loop (e.g. due to alow-quality RF choke, or due to two impedance mismatches) can permit theoscillator to hop to a frequency which is determined (at least partly)by a harmonic of the spurious resonance, in which case the degree towhich the oscillator frequency has been pulled by the changing load willbe obscured.

To avoid such problems in a load-pulled system, a small series resistorcan be interposed in the RF output of the oscillator, before themeasurement section connection. This resistor adds a small amount ofdamping, which helps to suppress oscillation to secondary frequencies).

To further improve stability, a shunt resistior can be attached to theRF output of the load-pulled oscillator. This resistor adds tostability, by fixing a maximum magnitude for the load impedance seen atthe RF output line.¹⁵

Background: Other Approaches to Electrical Characterization

Various types of apparatus have been proposed for measuring theconcentration of one substance in another, particularly theconcentration of a liquid or flowable substance in another liquid orflowable substance. Various devices which utilize the broad concept ofdetermining composition of matter by measuring changes in a microwavesignal are disclosed in U.S. Pat. Nos. 3,498,122 to Howard; 3,693,079 toWalker; 4,206,399 to Fitzky et al.; 4,311,957 to Hewitt et al.;4,361,801 to Meyer et al.; 4,240,028 to Davis Jr.; 4,352,288 to Paap etal.; 4,499,418 to Helms et al.; and 4,367,400 and 4,429,273, both toMazzagatti; all of which are hereby incorporated by reference.

Although various systems utilizing microwave transmissivity or signalalteration characteristics have been proposed in the prior art, certainconsiderations in utilizing microwave energy to detect the presence ofthe concentration of one medium in another have not been met by priorart apparatus. In particular, it is desirable in certain instances to beable to accurately measure, on a continuous bases, the concentration orchange in concentration of one fluid in another and particularly wherethe concentration of one fluid is a very low percentage of the totalfluid flow rate or fluid mixture quantity. It is also desirable that thesignal change caused by the presence of one substance or medium inanother be easily measured and be relatively error free, again,particularly in instances where measurements of low concentrations ofone substance such as a fluid in another substance such as another fluidare being taken. Moreover, it is important to be able to transmit themicrowave signal through a true cross section of the composition beingsampled or measured to enhance the accuracy of the measurement.

Typical systems for capacitive based measurement have a capacitiveelement, used for parameter determination, as part of the resonantfeedback loop around an active device. This method works well with verylow loss systems, but oscillation ceases with even slightly lossymeasurements. As the frequency is increased into the microwave region,it becomes difficult to configure the resonant feedback loop due to theincrease in loss versus frequency and the wavelength becoming comparableto the path length. In this case the frequency is changed directly bythe resonance change in the feedback loop which includes the elementthat consists of the sample to be measured. This frequency change islimited to the characteristics and loss of the feedback path and canonly be changed over a narrow frequency range with out cessation ofoscillations. This limits the measurement technique to small samples ofvery low loss.

At higher frequencies (above approximately 100 MHz), the capacitivemeasurement technique fails to work, due to line lengths and straycapacitances. At such frequencies resonant cavity techniques have beenemployed. (For example, a sample is placed in a resonant cavity tomeasure the loss and frequency shift with a external microwave frequencysource that can be swept across the resonance with and without thesample in the cavity.) This method uses a highly isolated microwavefrequency source which is forced by the user (rather than being pulledby the changing resonance) to change it frequency. This technique toomeets substantial difficulties. For example, the use of multipleinterfaces without a microwave impedance match at each interface causesextraneous reflections, which tend to hide the desired measurement data.This technique too gives errors with very lossy material, but in thiscase it is due to the very rounded nature of the resonance curve (whichis due to the low Q of the loaded cavity). This rounded curve makes itdifficult to determine both the center frequency and the 3 dB rollofffrequency closely enough to be accurate in the measurement.

Another technique which is used encompasses the use of the very sharprise time pulse to obtain time domain data, from which frequency domainvalues are then derived through transformation techniques.

In U.S. Pat. No. 4,396,062 to Iskander, entitled Apparatus and Methodfor Time-Domain Tracking of High-speed Chemical Reactions, the techniqueused is time domain reflectometry (TDR). This contains a feedback systemcomprising a measurement of the complex permittivity by TDR means whichthen forces a change in frequency of the source which is heating theformation to optimize this operation. Additionally it covers themeasurement of the complex permittivity by TDR methods.

U.S. Pat. No. 3,965,416 to Friedman appears to teach the use of pulsedrivers to excite unstable, bi-stable, or relaxation circuits, andthereby propagate a pulsed signal down a transmission line whichcontains the medium of interest. The pulse delay is indicative of thedielectric constant of the medium. As in all cases, these are eithersquare wave pulses bout zero or positive or negative pulses. The circuitis a pulse delay oscillator where the frequency determining element is ashorted transmission line. The frequency generated is promoted andsustained by the return reflection of each pulse. The circuit will notsustain itself into a load that is lossy, since the re-triggering willnot occur without a return signal of sufficient magnitude. In addition,the circuit requires a load which is a DC short in order to complete theDC return path that is required for re-triggering the tunnel diodes.

The frequencies of operation of any pulse system can be represented as aFourier Series with a maximum frequency which is inversely dependentupon the rise time of the pulse. Therefore, the system covered in theFriedman patent is dependent upon the summation of the frequencyresponse across a wide bandwidth. This causes increased distortion ofthe return pulse and prevents a selective identification of thedielectric constant versus frequency. This also forces a design of thetransmission system to meet stringent criteria to prevent additionalreflections across a large bandwidth.

The low frequency limit of the TDR technique is determined by the timewindow which is a function of the length of the transmission line. Theupper extreme is determined by the frequency content of the appliedpulse. In the case of this pulse delay line oscillator, the upperfrequency is determined to a greater extent by the quality of impedancematch (the lack of extra reflections) form the circuit through thesubstance under study. These extra reflections would more easily upsetthe re-triggering at higher frequencies.

In one case (FIG. 1 of Friedman) the return reflection initiates a newpulse from the tunnel diode and therefore sets up a frequency (pulserepetition rate) as new pulses continue to be propagated. This is inessence a monostable multivibrator with the return reflection being thetrigger. The problem implied, but not completely covered with thisapproach, is that due to the delay in pulses, the pulse train canoverlap and cause multiple triggers to occur. These are caused by there-reflections of the original parent pulse. An additional problem iswith very lossy dielectrics, which will not provide enough feedbacksignal to initiate the next pulse. If the dielectric medium is of highenough dielectric constant to contain more than one wavelength, or ifthe dielectric constant of the samples vary greatly, multiple returnreflections will alter the behavior of the circuit to render it uselessdue to the interfering train of return and parent pulses.

FIG. 3 is Friedman shows a bistable multivibrator which senses thereturn pulse by sampling the feeding back enough phase shifted voltageto re-set the tunnel diodes. Since this device is also dependent uponthe return to trigger or re-trigger the parent pulse, it suffersproblems with lossy dielectrics and high dielectric constant mediums.

To overcome these problems, the relaxation oscillator of FIG. 4 ofFriedman was proposed that contains a RC (resistor/capacitor timing)network which will maintain the generation of pulse trains usingresistor 76 and capacitor 78 with the dielectric filed transmission lineaffecting the regeneration of the pulses as the reflected parent pulsevoltage is returned. Since the RC time constant is defining the basicrepetition rate, some improvement is obtained in reducing second ordereffects. The transmission line is still an integral part of the overallrelaxation oscillator and lossy dielectrics may cause irregular circuitresponse. The proposed inverting amplifier as the pulse generator willnot function at above approximately 1 MHz in frequency due to thecharacteristics of such inverting amplifiers. The tunnel diode can pulseup to a 100 MHz rate.

By contrast, the innovative system embodiments disclosed in the presentapplication and its parents differ from the known prior art in using amicrowave frequency generated by a free running sine wave oscillator.The preferred oscillator has the versatile capability to work into awide variety of transmission lines or other load impedance withoutgeneration of spurious data or cessation of oscillations. It willcontinue to oscillate with very lossy dielectrics. It is not arelaxation oscillator or a multivibrator. The frequency of theun-isolated oscillator is dependent upon the net complex impedance ofthe transmission line and will work into an open circuit as well as ashort circuit. The net complex impedance at the frequency of operationof the oscillator looking at the transmission line containing the mediumof interest results in stable oscillations through pulling of theunisolated oscillator. Only one frequency at any one time is involved inthe disclosed system proposed (not counting harmonics which are at least10 dB down from the fundamental). This provides for well definedinformation and eases the transmission design criteria. This alsoprovides for evaluation of the dielectric constant versus frequencywhich can improve resolution of constituents or ionic activity.

Another important difference from prior art is the separation of theload of interest from the resonant circuit proper. The configurationused isolates the two through the transistor. It is the non-linearbehavior of the transistor that provides the changes in frequency as theload is changed. The loop gain of an oscillator must be unity with 180°phase shift. The initial gain of the transistor must be greater beforeoscillation begin in order for the oscillator to be self starting. Thisextra gain is reduced to unity by the saturation of the active deviceupon establishment of the oscillator frequency. Saturating a devicechanges the gain (and accordingly the phase since it is non-linear) tomaintain oscillations as the load changes. This will continue as theload changes as long as the transistor has appropriate phase andavailable gain to satisfy oscillations.

SUMMARY OF THE INVENTION Planar Probe

The present application discloses a planar probe which can be readilyinserted into a variety of materials in solid, liquid, gas or plasmaphase. This probe provides a "single-ended" coupling element whichpermits load-pull measurements to be made on an increased variety ofmaterials. As with the coaxial configuration, oscillator frequency canbe monitored directly, or in combination with insertion loss.

A variety of probes have been suggested for industrial microwaveapplication. See, e.g., Nyfors & Vainikainen, INDUSTRIAL MICROWAVESENSORS (Artech 1989), which is hereby incorporated by reference, andespecially pages 226-228 thereof. Many of these probes can be used forload-pull application, but none of these probes are ideally suited: forexample, the stripline probe shown on page 226 (FIG. 4.15) shieldssignal propagation in one direction, and thus lessens coupling to amedium to be sampled, which is undesirable in most load-pullapplications.

By contrast, the disclosed planar probe provides very efficient couplingto the surrounding medium, in a compact, rugged, and easily manufactureddesign. The disclosed planar probe, unlike many previous arrangements,provides a single-ended structure for coupling to a material under test.

Such a probe turns out to provide very high sensitivity. A short lengthof transmission line in a plane structure has been found to beapproximately 3 to 10 times as responsive (per unit length) as a sectionof coaxial line structure (like that shown in the previous load-pullapplications cited above). This may be due to the third dimensionalvariable caused by the micro strip structure having one propagationvelocity and the fluid under measurement having a second propagationvelocity, with the resulting phase shifts interacting down the length ofthe transmission line. This effect will typically give a non-linearphase dispersion versus frequency and material changes. Full modellingof this structure is difficult, because it must be treated as athree-dimensional structure rather than a two dimensional structure.Moreover, the lossiness of the immediate environment of the striplinemay determine whether propagation occurs predominantly in slow-wave orfast-wave mode.¹⁶

The transmission line is preferably nonresonant over the full range offrequencies of interest, although it may (less preferably) haveresonances at other frequencies.

In one embodiment, such a probe is mounted on a standard flange for easyinsertion into a process stream.

The dimensions of the probe are not particularly critical. Thetransmission line should preferably have an electrical length of atleast several half-wavelengths, but can be made long if highersensitivity is desired.

Note that the probe does not include a large amount of structure norelectronics. Thus, for many applications, the probes can be discardedafter each use.

The simplest substrate is simply fired high-density alumina (essentiallyAl₂ O₃). This is commercially available, and is commonly used formicrowave circuits (due to its desirable low-loss properties). This maybe used bare, or with a passivating coating. Alternatively, the probesubstrate can be assembled to a solid dover, such as low-densityalumina, fired alumina, other ceramic materials, or even fiberglass.

The probe can be used "bare", i.e. with the leads exposed, ifsufficiently inert metallization is used, e.g. gold or aself-passivating metallization such as stainless steel. Alternatively, athin applied passivation layer can be used, such as plasma-deposedperfluorocarbon.

However, in alternative embodiments (as discussed below), substrateswith other selective absorption properties can be used instead.

A significant advantage of the planar probe over the coaxialconfigurations previously discussed is that a very wide bandwidth can beused, even with materials of very high permittivity. This is because ofthe low loss and short length of the planar structure. Coaxial operationlimits the frequency range which can be used, because the reduceddiameter of the coaxial measurement section (necessary for operation athigh frequencies) will cause significant pressure drop, and may causeprecipitation and clogging in mixtures containing large volumes ofparticlates.

Among the disclosed inventions is provided a method for detecting thecomposition and microstructure of materials, comprising the steps of:providing a tunable oscillator which is connected to be pulled by thevarying susceptance seen at a load connection thereto; connecting theload connection to the material under test through a single-ended probewhich includes a substantially planar metal film structure which ispatterned to provide a transmission line extending from the connection;and observing changes in the frequency of the oscillator.

Among the disclosed inventions is provided an electricalcharacterization system in which a single-ended planar probe, containinga transmission line of at least several half-wavelengths, is placed inproximity to a material to be characterized and is electrically coupledto a load-pulled voltage-controlled oscillator. The frequency responseof the oscillator is then observed as the tuning voltage is varied.

SUMMARY OF THE INVENTION Tapered Probe

The present invention discloses a probe which can be readily insertedinto a variety of materials in solid, liquid, gas or plasma phase. Thisprobe provides a "single-ended" coupling element which permits load-pullmeasurements to be made on an increased variety of materials.

A basic requirement of many applications is the need for measurement ofmaterials having a wide range of dielectric constant (ε from 1 to 180)using a single transmission line section. This may create problems inlaunching the electromagnetic energy into a different dielectric medium.Without some help in making a graceful transition from one propagationmedium to another (at a very different dielectric constant), the energywill simply be reflected.

The present disclosure teaches that a single-ended probe using a gradedimpedance (achieved by a planar tapered line or otherwise) can beparticularly advantageous for coupling a load-pulled oscillator to amaterial system to be monitored. In alternate emolument, such probes canalso be used for RF sensing in other electrical configurations, usingstandard instrumentation in the microwave industry as a part of materialcharacterization problems. Such embodiments are less preferable, but canstill confer some of the advantages of the claimed inventions.

To solve this coupling problem, the disclosed inventions provide atapered structure which performs an extended impedance transformationacross a significant distance while coupled to the material under test.This solves the problem of coupling to the dielectric material. It alsohelps to solve the problems of lossy materials (such as salt water),where the lossiness of the material can make it difficult to obtain anyusable signal at all.

However, it should be noted that, as the dielectric constant increases,the length appears shorter due to the rapid decrease of electricallength due to lower impedance. Thus, the physical length of a taperedprobe may need to be longer than that of a corresponding straight probe.

The preferred approach to this is a "tapered planar" structure, i.e. aplanar probe with a taper imposed on the trace geometries. An example ofthis is shown in FIG. 5B. This provides a compact single-ended probewhich can be used for load-pull or the characterization of widelyvarying material streams.

Tapered lines have been used before for impedance matching in microwavecircuits--see, e.g. U.S. Pat. Nos. 5,119,048 and 4,568,889, which arehereby incorporated by reference. However, the present disclosureteaches that tapered lines have substantial advantages for"single-ended" coupling to an unknown material, or as a general-purposetool for coupling to a variety of material with widely varyingpermittivity and loss characteristics. The prior uses of tapered lineswere primarily for impedance matching between structures or betweenfixed dielectrics, and not for launching a wave into a varyingdielectric stream. Some impedance matching structures have ben used inslow wave structures, but again these are fixed situation matches andare not defined for large variable differences using the samestructures. Similarly, transformation structures in waveguides are notfully analogous: A waveguide is operating for each mode the thefrequency ranges where that mode is possible. The "wave impedance"concept provides a good analytical too for such structures, but lead tosome difficult analysis, since the wave impedance depends on thefrequency of operation, the guide dimensions, and the mode. The actualwavelength in the guide is dependent on the cutoff frequency, but acoaxial line has cutoff frequency of infinity.

Coaxial Structure with Tapered Sheath

An alternative embodiment provides a coaxial sampling chamber whichincludes a tapered dielectric sheath around the central rod at the pointof fluid entry. This provides for a gradual interface charge andtherefore will allow enough propagation to occur in high ε_(n) materialsin order to give a measure of ε_(n).

In the initial launch point into the fluids the sheath materialdominates the impedance function and vice versa at the other end. Forlow dielectric fluids and taper section, the occlusion of the fluids atthe launch mediates the resultant dielectric constant of the crosssection at that point to roughly that of the taper.

The taper coaxial structure provides a significant fraction of awavelength for the field pattern to conform to the new velocity andconfiguration. The impedance function then becomes a gradient whichprovides a transition from a 50 ohm system impedance to whatever theresultant impedance that the dielectric material in the coaxial sectiondefines.

According to one alternative teaching, the transition section iselectrically sufficient short (at the operating frequencies used) toprevent knees from ever occurring (no matter how high the ε_(n)) willgive a set of curves which are monotonic with ε_(n).

Among the disclosed inventions is provided a system for detecting thecomposition and microstructure of materials, comprising: an RFoscillator, which includes a gain element capable of providingsubstantial gain at frequencies greater than 10 MHz; a feedback path,coupling the output of the gain element to the input thereof, thefeedback path including a tunable resonant circuit; an electromagneticpropagation structure which is RF-coupled to load the oscillator and inwhich electromagnetic wave propagation is electrically loaded by aportion of the material to be characterized, the propagation structureincluding a distributed impedance transformation section which includesat least one tapered element and which is itself also electricallyloaded by proximity to a portion of the material; and circuitryconnected to monitor the frequency of the oscillator to ascertainchanges in the composition and/or microstructure of the material.

Among the disclosed inventions is provided a single-ended RF probe, forproviding a bidirectional RF interface to unknown materials of widelyvarying permittivity, comprising: an external RF connection mechanicallyconnected to a support structure; and a patterned and substantiallyplanar conductive structure which is electrically connected to theconnection and mechanically supported by the support structure; theconductive structure being shaped to provide a distributed impedancetransformation section therein.

Among the disclosed inventions is provided a method for detecting thecomposition and microstructure of materials, comprising the steps of:providing a tunable oscillator which is connected to be pulled by thevarying susceptance seen at a load connection thereto; connecting theload connection to the material under test through a single-ended probewhich itself includes a distributed impedance transformation sectionwhich is itself electrically loaded by proximity to a portion of thematerial under test; tuning the oscillator over a range of frequencies;and observing changes in the frequency of the oscillator in response tothe tuning step.

Among the disclosed inventions is provided an electricalcharacterization system in which a load-pulled voltage-controlledoscillator is coupled to a material to be characterized by a probe whichcontains a distributed impedance transformation section which includesat least one tapered element and which is electrically loaded byproximity to a portion of the material. The frequency response of theoscillator is then observed as the tuning voltage is varied.

SUMMARY OF THE INVENTION Probe with Selective Absorber

The present application discloses structures and methods for enhanced RFdetection using chemically selective coatings on an RF probe. Thedisclosed inventions provide new methods for monitoring andcharacterization, using microwave energy, for use in the analysis ofmultiple component and bio-chemical systems.

Various electrode and chemical assay systems have been used in the pastfor specific measurements in organic systems. These methods weretypically very slow and sensitive to operator and technique. Generally,most laboratories were forced to continue to rely on expensive andelaborate HPLC (High-Pressure Liquid Chromatography) and other primarytype instrumentation for these measurements. This prevented rapidturnaround for process control.

The new technology disclosed herein can measure a vast list of specificorganic species using immobilized enzymes, glucose in blood chemistry,lactic acid in muscle tissue, immunological tests, cancer cytology, andobservation of catalytic action.

Additional special applications include moisture sensing of grains andbulk materials using absorbing/desorbing ceramic material. This wouldmake these measurements possible and simple even though the bulkmaterial's packing density has prevented such measurements in the past.Since the material arrives at a specific level of moisture with itssurroundings, the bulk density is not important.

An important part of this method are the materials used to place themicrowave structure on. The substrate material can be anything whichwill support an electromagnetic field and have specific properties for achemical structure. Examples include zeolites, ceramics with specificabsorptions, doped semiconductors which increase/decrease theirconductivity/dielectric constant with absorption. The sue of enzymesembedded in a porous structure which are altered by selective substancesmay also be possible. This change in the enzyme structure would bevisible with the load pull scheme. If a substrate was embedded or coatedwith a material which would deteriorate with selective absorption, themonitoring of the degradation wold give rise to determination of theamount of the chemical present.

For another example, zirconia has unusual properties with oxygen at hightemperatures. It forms a ion exchange with oxygen molecules which isused to measure oxygen content of gas streams especially in cars andstack emission monitoring. Use of this as a substrate could possiblyhave unique characteristic changes when the O₂ is present.

In the medical, food and pharmaceutical industries, it can beadvantageous to implement this idea with throwaway substrates.

A particular advantage of the absorber-coated probe is that it can bedesigned to be self-calibrating. By contrast, other probes may need tobe calibrated with a sample which is (or approximates) the material inquestion.

Humidity Sensing

The simplest application of selective absorption is for humiditysensing, e.g. using an absorber of low-density Al₂ O₃ (alumina). Aluminawill equilibrate to a moisture concentration which is exactlyproportional (within a certain range) to the ambient humidity. (Theinteraction between alumina and water is typical of many materialssystems, where the relative equilibrium concentrations of absolute S inmaterials A and B are linearly related by a segregation coefficientK=[S]_(A) /[S]_(B).)

However, the present invention does not require as much time as would beneeded for equilibration. Instead, the rate of uptake of humidity by theabsorber is differentially monitored, and this provides a fastmeasurement which also is related to the ambient humidity.

Note that the absorbent material need not be so readily reversible. Forexample, there is a vast literature on customizing zeolite structures tomake "molecular sieves." However, the affinity of many such structuresfor their complementary substance is so high that the adsorbate is verytightly bound. Thus, a zeolite absorber may need to be periodicallypurged, or simply discharged when saturated.

In a further alternative embodiment, where an active matrix materialsuch as zeolite is to be used for moisture measurement in grains andgood solids, a "zip open" sealed bag can be useful for field use.

Among the disclosed inventions is provided a system for detecting thecomposition and microstructure of materials, comprising: an oscillator,which includes a gain element capable of providing substantial gain atfrequencies greater than 100 MHz, and a feedback path, coupling anoutput of the gain element to an input thereof, the feedback pathincluding a tunable resonant circuit; and an electromagnetic propagationstructure which is RF-coupled to load the oscillator and in whichelectromagnetic wave propagation is electrically loaded by a portion ofthe material to be characterized, the propagation structure beingmechanically connected to a selective absorption material, which isselective to preferentially absorb a predetermined target species, andelectrically configured to provide efficient capacitive coupling to thepropagation structure; and circuitry connected to monitor the frequencyof the oscillator to ascertain changes in the composition ormicrostructure of the material.

Among the disclosed inventions is provided a single-ended RF probe, forproviding a bidirectional RF interface over a range including at leastone predetermined operating frequency, to detect the presence of atleast one target species in a quantity of material, comprising: anexternal RF connection mechanically connected to a support structure;and a conductive structure which is electrically connected to theexternal connection and technically supported by the support structure,and which provides a transmission line extending from the externalconnection; and a selective absorption material, which is selective topreferentially absorb a predetermined target species, and which ismechanically connected to the support structure in a relation whichprovides efficient capacitive coupling to the selective transmissionline.

Among the disclosed inventions is provided a method for detecting thecomposition and microstructure of materials, comprising the steps of:providing a tunable oscillator which is connected to be pulled by thevarying susceptance seen at a load connection thereto; connecting theload connection to the material under test through a single-ended probewhich includes a substantially planar metal film structure which ispatterned to provide a transmission line extending from the externalconnection, and which also includes a selective absorption material,which is selective to preferentially absorb a predetermined targetspecies, and which is mechanically affixed to the probe to provideefficient capacitive coupling to the transmission line; and observingchanges in the frequency of the oscillator.

Among the disclosed inventions is provided an electricalcharacterization system in which a single-ended planar probe, containinga transmission line of at least several half-wavelengths and a selectiveabsorption material to which a species of interest will segregate, isplaced in contact with a material to be characterized, and is alsoelectrically coupled to a load-pulled oscillator.

SUMMARY OF THE INVENTION Probe with Integrated Heater

A further embomdent provides an RF probe which not only includes aselective-absorbing material (such as alumina), but also includes aheater for causing desorption of the absorbed material. This permits theheater to be "cycled" efficiently.

This could be embedded in the ground plane or placed on the backside ofthe substrate. This heater would be activated at either a set value offrequency change or at time intervals. During the on cycle the change inthe material can be simultaneously monitored by the same load pulledoscillator to determine when the regeneration point has been reached orto indicate to an operator that the time to replace the probe andmaterial has arrived.

This embomdent also permits some aggressive absorbing materials (such ashigh-affinity zeolites) to be used for selective absorption.

This embodiment is particularly attractive for field measurement ofhumidity, but can also be used for measurement of other substances.

In some applications, this heater can also be used to providetemperature regulation of the probe's immediate environment, if thematerial under test would not provide a heavy thermal load. For example,this may be useful where the sample is gaseous and of variabletemperature.

In the presently preferred embodiment, separate leads are provided topower a resistive heater in a planar structure. However, in analternative embomdent a resistive heater can be driven by a DCcomponents on the coaxial line (if the power detection diode is notused). In this embodiment, an isolating inductance can be used with theheater to avoid resonances.

During each absorption cycle, the rate of uptake can be measured usingtime-differentiated measurements. An integral is accumulated to providean index of the total loading of the absorber. The relation between thisintegral and the rate of uptake provides an index of the ambientconcentration. When the integral exceeds a certain threshold, thisindicates that the absorber is becoming fully loaded. The heater is thenactivated to refresh the absorber and start the cycle again.

Among the disclosed inventions is provided a system for detecting thecomposition and microstructure of materials, comprising: an oscillator,which includes a gain element capable of providing substantial gain atfrequencies greater than 100 MHz, and a feedback path, coupling anoutput of the gain element to an input thereof, the feedback pathincluding a tunable resonant circuit; and an electromagnetic propagationstructure which is RF-coupled to load the oscillator and in whichelectromagnetic wave propagation is electrically loaded by a portion ofthe material to be characterized, the propagation structure beingmechanically connected to a selective absorption material, which isselective to preferentially absorb a predetermined target species, andelectrically configured to provide efficient capacitive coupling to thepropagation structure, and also to a heater integrated with thepropagation structure in a common package; and circuitry connected tomonitor the frequency of the oscillator to ascertain changes in thecomposition or microstructure of the material, and to activate theheater selectively which absorption material has become loaded.

Among the disclosed inventions is provided a single-ended RF probe, forproviding a bidirectional RF interface over a range including at leastone predetermined operating frequency, to detect the presence of atleast one target species in a quantity of material, comprising: anexternal RF connection mechanically connected to a support structure; aconductive structure which is electrically connected to the externalconnection and mechanically supported by the support structure, andwhich provides a transmission line extending from the externalconnection; and a resistive heater which is mechanically supported bythe support structure, and connected to receive a drive current; and aselective absorption material, which is selective to preferentiallyabsorb a predetermined target species, and which is mechanicallyconnected to the support structure in a relation which provide efficientcapacitive coupling to the transmission line.

Among the disclosed inventions is provided a method for detecting thecomposition of materials, comprising the steps of: providing a tunableoscillator which is connected to be pulled by the varying susceptanceseen at a load connection thereto; connecting the load connection to thematerial under test through a single-ended probe which includesconnecting the load connection to the material under test through asingle-ended probe which includes a conductive structure which ispatterned to provide a transmission line extending from the externalconnection, and which also includes a selective absorption material,which is selective to preferentially absorb a predetermined targetspecies and which is mechanically affixed to the probe to provideefficient capacitive coupling to the transmission line, and a resistiveheater which is integrated with the probe; and observing time-dependentchanges in the frequency of the oscillator to detect the rate of uptakeof the target species and the cumulative loading of the absorber; andactivating the heater, whenever the absorber becomes excessively loaded,to cause desorption of the target species.

Among the disclosed inventions is provided a single-ended RF probe whichcontains; a transmission line of at least several half-wavelengths; aselective absorption material to which a species of interest willsegregate; and a resistive heater; all integrated into a commonmechanical structure. The heater can be used to "unload" the absorptionmaterial, by driving off the target species from it. This isparticularly useful for humidity measurement.

SUMMARY OF THE INVENTION Monitoring Fermentation

The present application discloses processes for monitoring bulkfermentation, and for partially characterizing the composition of abatch fermentation, by observing the frequency of a load-pull oscillatorwhich is RF-coupled to the material under test (preferably by a simplesingle-ended RF probe).

Most pharmaceutical fermentations are done in a small batch mode wherethere is no flow. The planar probe structure is very conductive to thisapplication. The planar structure also lends itself to throw awayreplacement to maintain sensitivities and prevent bacteriological growthin these sensitive vats. Of course, sterile load-lock procedures arepreferably used for insertion of a sterile RF probe into a culture vat.

It should be noted that the disclosed methods are not only useful forpharmaceutical applications, but may also be useful in brewing,winemaking, and in food industry processes using biologically activeagents.

The disclosed methods also permit the biomass of a fluid stream to bemeasured. Thus metering of a starter culture can be optimized withoutwaste.

The disclosed methods also provide a direct test for yeast viability insolution. Thus the presence of yeast activity can be checked during theearly stages of fermentation, before the yeast mass has multipliedsufficiently to be unmistakably active.

Among the disclosed inventions is provided a method for monitoring thestatus of a fermentation process, comprising the steps of: introducingselected active microorganisms into an aqueous solution containingnutrient substances, and isolating the solution in a substantiallysterile vat; electromagnetically coupling a RF probe to the solution inthe vat, and connecting the probe to load an oscillator operating atmore than 100 MHz, with no RF buffer stage being interposed between theoscillator and the probe; and observing time-dependent changes in thefrequency behavior of the oscillator, to indicate changes in thecomposition of the solution.

Among the disclosed inventions is provided a method for initiating afermentation process, comprising the steps of: introducing selectedactive microorganisms from a starter culture into a nutrient solution,while also monitoring the flow rate of the introducing step andmonitoring the frequency of an RF oscillator which is connected to thestarter culture through a RF probe which is electromagnetically coupledby proximity to be loaded by the starter culture, with no RF bufferstage being interposed between the oscillator and the probe; andterminating the flow to provide a desired total biomass transferred fromthe starter culture into the nutrient solution.

Among the disclosed inventions is provided a method for monitoring bulkfermentation, and for partially characterizing the composition of abatch fermentation, by observing the frequency of a load-pull oscillatorwhich is RF-coupled to the material under test (preferably by a simplesingle-ended RF probe).

SUMMARY OF THE INVENTION Monitoring Curing/Crystallization

The present application discloses processes for monitoring the state ofcuring (or microcrystalline change) of solid materials, by observing thefrequency of a load-pull oscillator which is RF-coupled to the materialunder test (preferably by a simple single-ended RF probe).

One area where this technique is of particular interest is in monitoringthe curing of shaped aerodynamic composite materials.

Most pharmaceutical fermentations are done in a small batch mode wherethere is no flow. The planar probe structure is very conductive to thisapplication. The planar structure also lends itself to throw awayreplacements to maintain sensitivities and prevent bacteriologicalgrowth in these sensitive vats. Of course, sterile load-lock proceduresare preferably used for insertion of a sterile RF probe into a culturevat.

It should be noted that the disclosed methods are not only useful forpharmaceutical applications, but may also be useful in brewing,winemaking, and in food industry processes using biologically activeagents.

The disclosed methods also permit the biomass of a fluid stream to bemeasured. Thus metering of a starter culture can be optimized withoutwaste.

The disclosed methods also provide a direct test for yeast viability insolution. Thus the presence of yeast activity can be checked during theearly stages of fermentation, before the yeast mass has multipliedsufficiently to be unmistably active.

Among the disclosed inventions is provided a method for monitoring thestatus of a fermentation process, comprising the steps of: introducingselected active microorganisms into an aqueous solutoin containingnutrient substances, and isolating the solution in a substantiallysterile vat; electromagnetically coupling a RF probe to the solution inthe vat,and connecting the probe to an oscillator operating at more than100 MHz, with no RF buffer stage being interposed between the oscillatorand the probe; and observing time-dependent changes in the frequencybehavior of the oscillaotr, to indicate changes in the compostion of thesolution.

Among the disclosed inventions is provided a method for initiating afermentation process, comprising the steps of: introducing selectedactive microorganisms from a start culture into a nutrient solution,while also monitoring the flow rate of the introducing step andmonitoring the frequency of an RF oscillator which is connected to thestarter culture through a RF probe which is electromagnetically coupledby proximity to be loaded by the starter culture, with no RF bufferstage being interposed bewteen the oscillator and the probe; andterminating the flow to provide a desired total biomass transferred fromthe starter culture into the nutrient solution.

Among the disclosed inventions is provided a method for monitoring bulkfermentation, and for partially characterizing the composition of abatch fermentation, by observing the frequency of a load-pull oscillatorwhich is RF-coupled to the material under test (preferably by a simplesingle-ended RF probe).

SUMMARY OF THE INVENTION Monitoring Curing/Crystallization

The present invention discloses processes for monitoring the state ofcuring (or microcrystalline change) of solid materials, by observing thefrequency of a load-pull oscillator which is RF-coupled to the materialunder test (preferably by a simple single-ended RF probe).

One area where this technique is of particular interest is in monitoringthe curing of shaped aerodynamic composite materials. at more than 100MHz, with no RF buffer stage being interposed between the oscillator andthe probe; and observing time-dependent changes in the frequencybehavior of the oscillator, to detect changes in the composition and/ormicrocrystalline structure of the body.

Among the disclosed inventions is provided a method for controlling aprocess of curing a predetermined solid material, comprising the stepsof: combining precursor components to provide a body of the material;electromagnetically coupling a single-ended RF probe to the body, andconnecting the probe to load an oscillator operating at more than 100MHz, with no RF buffer stage being interposed between the oscillator andthe probe; and observing time-dependent changes in the frequencybehavior of the oscillator, to detect changes in the composition and/ormicrocrystalline structure of the body.

Among the disclosed inventions is provided a method for monitoring thestate of curing (or microcrystalline change) of solid materials, byobserving the frequency of a load-pull oscillator which is RF-coupled tothe material under test (preferably by a simple single-ended RF probe).

SUMMARY OF THE INVENTION Monitoring Food Composition and Process Stageof Food Materials

The present application discloses processes for monitoring the state ofprocessing of, and for partially characterizing the composition of, foodand feed products, by observing the frequency of a load-pull oscillatorwhich is RF-coupled to the material under test (preferably by a simplesingle-ended RF probe).

Conventional process control in the food industries is almost entirelyoff-line (using laboratories to test samples). On-line controls areordinarily limited to temperature, flow meters, viscosity, and mass(weighing systems). Processes are usually "recipes" of weights, times,and temperatures. This is because foodstuffs are chemically verycomplex, so that conventional high-tech methods (such as chromatographsand near IR spectroscopy) are not usually as adaptable to one lineprocess control as in the "regular chemical" industry. The materials aremolecularly too complex.

Therefore, laboratory analysis must be used to measure (or infer) aprocess condition. Items as carbohydrates, fats, protein, fiber content,ash content, mineral content are done by conventional "wet" analysis.These lab methods are usually

1. Refractometry

2. Photoelectric Calorimetry

3. Some spectrophotometry

4. Some polarimetry

5. Melting/softening points

6. Viscometry

7. Conductivity

8. Some Chromatography

9. Titrations

10. Mass/Loss gravimetric methods

11. Solvent extractions techniques

Sometimes these are indirect measurements. For example, viscosity may beused to infer water content or gelatinization of starch (cooking). Watercontent of various components is a major item of interest/control. Thisis usually measured by heating a sample and measuring the weight loss.Color is used to determine proper cooking times for caramelization ofstarch/flour products.

By contrast, the disclosed methods permit direct real-time measurementof the molecular changes.

In one aspect of this, melting and softening can be measured directly,and correlation with temperature will then give an direct measurementsof process states.

Given a generally known process flow, the present invention provides newmethods for monitoring the composition of the flow. For example, thedisclosed inventions permit real-time non-contaminating measurement ofwater content, or fat content, or both in a stream of ingredients or ina stream of processed food products.

Given a generally known process flow, the present invention alsoprovides new methods for monitoring the degree of cooking of the flow.As the following results show, the molecular changes in starches whichare caused by cooking can be directly detected, and the molecularchanges in meats which are caused by cooking can also be directlydetected. This provides efficient endpoint detection for foodprocessing.

The simplest way to use this monitoring technique analytically is tolook at the time derivative of the measured RF frequencies: a certainpercentage decrease in the rate of change can be used for an endpointsignal, to terminate a batch cooking state. (Of course, this percentagedecrease wold be customized for a particular process, and would allowfor continued cooking as the temperature of the food materials is rampeddown.)

Among the disclosed inventions is provided a method for processing foodand analogous materials, comprising the steps of: providing multipleflows if ingredient materials; electromagnetically coupling asingle-ended RF probe to at least one the flow of ingredient materials,the probe being electrically connected to load a free-running RFoscillator, with no RF buffer stage being interposed between theoscillator and the probe; and observing the frequency behavior of theoscillator, to detect variation in the composition of the respectiveflow of ingredient materials; dynamically controlling the flows of thematerials in accordance with results of the observing step; andcombining and processing the flows of ingredient materials to provide afood product.

Among the disclosed inventions is provided a method for drying organicmaterials, comprising the steps of: providing a flow of a material whichvaries in water content; electromagnetically coupling a RF probe to theflow, the probe being electrically connected to load a free-running RFoscillator, with no RF buffer stage being interposed between theoscillator and the probe; observing the frequency behavior of theoscillator, to detect the moisture content of the flow; and adding waterto the flow whenever the observing step indicates that the moisturecontent of the flow is below a target level; and drying the flow in adryer stage; whereby the moisture content of the flow is dynamicallycontrolled to be high enough to prevent clogging of the dryer, but nohigher than necessary for reliable operation.

Among the disclosed inventions is provided a method for cooking food andanalogous materials, comprising the steps of: introducing a mixture ofpredetermined ingredients into a cooking vessel; applying heat to thevessel in a controlled temperature-versus-time relationship, to cook themixture; electromagnetically coupling a RF probe to the mixture in thevessel, and connecting the probe to load an oscillator operating at morethan 100 MHz, with no RF buffer stage being interposed between theoscillator and the probe; observing the frequency behavior of theoscillator, to detect changes in the molecular composition and/orconformation of the mixture; and unloading the bat at a time which is atleast partially determined by the results of the observing step.

Among the disclosed inventions is provided a methods for monitoring thestate of processing of, and for partially characterizing the compositionof, food and feed products, by observing the frequency of a load-pulloscillator which is RF-coupled to the material under test (preferably bya simple single-ended RF probe).

SUMMARY OF THE INVENTION Patch Probe

In many applications the avoidance of direct contact with the materialsunder test is overwhelmingly desirable, to prevent contamination.

The present application discloses a noninvasive RF probe which can bereadily coupled, through a dielectric window, to a material under test.This probe provides a "single-ended" isolated-coupling element whichpermits load-pull measurements to be made on an increased variety ofmaterials. The electrical configuration of this probe is like that of apatch antenna,¹⁷ and hence this probe may be referred to as a "patchprobe". The patch probe is inherently less sensitive than a probe whichis directly immersed in or inserted into the material under test, butmay be sufficiently sensitive for many applications.

A planar probe can also be used for coupling through a window. In thiscase the planar probe would be placed flat against the window. However,the patch probe is preferred for such applications.

Among the disclosed inventions is provided a system for detecting thecomposition and microstructure of materials, comprising: an oscillator,which includes a gain element capable of providing substantial gain atfrequencies greater than 100 MHz, and a feedback path, coupling anoutput of the gain element to an input thereof, the feedback pathincluding a tunable resonant circuit and a patch antenna which isRF-coupled to load the oscillator and which is placed in proximity to aportion of the material to be characterized so that electromagnetic wavepropagation in the antenna is electrically loaded thereby; and circuitryconnected to monitor the frequency of the oscillator to ascertainchanges in the composition or microstructure of the material.

Among the disclosed inventions is provided a method for detecting thecomposition and microstructure of materials, comprising the steps of:providing a free-running oscillator which is connected to be pulled bythe varying susceptance seen at a load connection thereto; connectingthe load connection to the material under test through a patch antennawhich is RF-coupled to load the oscillator and which is placed inproximity to a portion of the material to be characterized so thatelectromagnetic wave propagation in the antenna is electrically loadedthereby; and observing changes in the frequency of the oscillator.

Among the disclosed inventions is provided an electricalcharacterization system in which a patch antenna, used as a single-endedRF probe, is placed sufficiently close to a material under test toachieve near-filed coupling thereto, and is also electrically coupled toa load-pulled oscillator.

SUMMARY OF THE INVENTION Load-Pull Analysis Method

The present application discloses a method for rapidly analyzing thestate of a given process. A load-pulled oscillator is coupled to thematerial under test, and is swept across a range of frequencies. Theoscillator frequency is swept, for example, by sweeping a tuningvoltage, applied to a varactor in the oscillator circuits, across apredetermined range. The oscillator is coupled to the material undertest by a probe which is electrically long (preferably at least severalhalf-wavelengths when fully loaded by the material under test). Thespecific conditions (probe type, physical conditions of coupling, andrange of tuning voltages or frequencies) will all have been previouslydefined, using the various considerations set forth in detail below. Theoscillator frequency is monitored while the tuning voltage is swept in apredetermined direction (up rather than down, for example.

For this defined set of conditions, each sweep of the tuning voltageV_(tun) will produce a corresponding range of oscillator frequencyvalues f_(osc). By integrating f_(osc) over the predetermined range ofV_(tun), a single derived index number results. This turns out to bevery useful in characterizing a given process under a given set ofconditions.

Part of the reason for this is that shifts in material composition whichproduce even very small shifts in permittivity will have the effect ofshifting the "knees" in the frequency curve. These knees, which arereadily visible in plots of oscillator frequency as a function of tuningvoltage, correspond to points where the oscillator phase goes through a180° transition. When this occurs, the oscillator will return to itsoriginal operating frequency, and this frequency is likely to shift.

In a typical application the oscillator's basic frequency can be forcedto change by the inclusion of a varactor (a voltage variable capacitor)in the primary resonant loop of the circuit. By applying a DC voltage onthis varactor, many oscillator scan be turned over an octave band. Inthe description above, the oscillator and load pull performance wasassuming a fixed frequency (no varactor) circuit. If the load was afixed length of lossless transmission line and the oscillator frequencywas forced by the applied voltage on the varactor as opposed to the loadpull phenomena, the "knees" would be seen as the phase seen at theoscillator was swept through 180° because of the effect of decreasedwavelengths at higher frequencies. The number of knees appearing in thevoltage vs frequency plot is dependent upon the dielectric constant ofthe medium in the transmission line, the length of the line and thefrequency.

Thus, simple data reduction can be performed to derive a single indexnumber for a given set of conditions. This is particularly useful wherea given system is being tracked over time, since the time-domainbehavior of the index number can easily be tracked. Thus, for instance,for endpoint detection in monitoring a batch process, the endpoint canbe identified when the index value has shifted by a certain percentagefrom its initial value and the rat of change has declined to a certainpercentage of its maximum value during the process run.

Among the disclosed inventions is provided a method for controlling aprocess, comprising the steps of: providing a voltage-controlledoscillator which is connected to be pulled by the varying susceptanceseen at a load connection thereto, and which is connected to be tuned bya tuning voltage applied thereto; connecting the load connection to anRF interface which is electrically loaded by proximity to materialundergoing the process; sweeping the tuning voltage across apredetermined range of voltages; integrating the oscillation frequencyof the oscillator, as a function of tuning voltage, across the range ofvoltages, to provide a process index value; comparing the process indexvalue with a known range of values for comparable process conditions;and taking action conditionally, within the process, in dependence onthe result of the comparing step.

Among the disclosed inventions is provided a process control method,wherein a load-pulled voltage-controlled oscillator is coupled throughan RF probe, without isolation, to a material in the process. Thefrequency response of the oscillator is then integrated over voltage, asthe tuning voltage is varied across a predetermined range. This integralgives a single "process index" value which is then used as a basis forconditional action on the process.

SUMMARY OF THE INVENTION Switchable Probe

A further disclosed innovation is a single-ended probe which includesmultiple transmission line segments, and which also includes an RFswitching element connected to permit switching between the twosegments.

If an RF switch (pin diodes) was used on the substrate to switch betweentwo lines, one could be an uncovered metal trace and the other could bea covered metal section with the covering being selective to aparticular chemical. This combination would provide a measurement of aspecific substance using the covered side of the probe, and once thiscomponent of the material under study is known an additional componentcould be derived from the response from the bare side of the probe. Forexample if the covered side was of the material to discern glucose in adextrose/glucose/water mixture, the bare side's additional informationwould provide for a solution to how much water was in the mixture.

This can also be used to provide spatially-resolved differentialmeasurement for detection of spatially-varying characteristics (e.g.material zone boundaries in a distillation or chromatographic column).

Among the disclosed inventions is provided a system for detecting thecomposition and microstructure of materials, comprising: an oscillator,which includes a gain element capable of providing substantial gain atfrequencies greater than 100 MHz, and a feedback path, coupling anoutput of the gain element to an input thereof, the feedback pathincluding a tunable resonant circuit; and an electromagnetic propagationstructure which is RF-coupled to load the oscillator and which includesan RF switch and first and second transmission line structures, theswitch being connected and configured to connect the first transmissionline structure to the external connection selectively under remotecommand; at least one of the transmission line structures beingpositioned so that electromagnetic wave propagation thereon can beelectrically loaded by proximity to a portion of the material to becharacterized; and circuitry connected to monitor the frequency of theoscillator to ascertain changes in the composition or microstructure ofthe material.

Among the disclosed inventions is provided a single-ended RF probe, forproviding a bidirectional RF interface to materials to be characterized,comprising: an external RF connection mechanically connected to adielectric support structure; and an RF switch mounted on the supportstructure and electrically connected to the external connection; andfirst and second transmission line structures, each connected to theswitch and mounted on the support structure; wherein the switch isconnected and configured to connect the first transmission linestructure to the external connection selectively, in accordance with abias signal received at the external connection.

Among the disclosed inventions is provided a method for detecting thecomposition and microstructure of materials, comprising the steps of:providing a tunable oscillator which is connected to be pulled by thevarying susceptance seen at a load connection thereto; connecting theload connection to the material under test through a single-ended probewhich includes an RF switch and first and second transmission linestructures, the switch being connected and configured to connect thefirst transmission line structure to the external connection selectivelyunder remote command; positioning the probe so that at least one of thetransmission line structures is electrically loaded by proximity to aportion of the material to be characterized; and observing changes inthe frequency of the oscillator, while switching the RF switch toactivate the first and second transmission lines alternately.

Among the disclosed inventions is provided a single-ended RF probe whichcontains an RF switch, and TWO transmission lines, all integrated into acommon mechanical structure. The two transmission lines can both becapacitively loaded by inserting the mechanical structure into amaterial under test, but the two lines have different couplingcharacteristics. (For example, one line may be coated with a selectiveabsorption material; or the two lines may merely be spatially separate.)Remote sensing electronics, such as a load-pulled oscillator, thus havean electrical interface through which to detect changes corresponding tothe properties of the material under test. The RF switch permitsadditional information to be gained by switching between the twotransmission lines.

BRIEF DESCRIPTION OF THE DRAWING

The present invention will be described with reference to theaccompanying drawings, which show important sample embodiments of theinvention and which are incorporated in the specification hereof byreference, wherein:

FIGS. 1A1 and 1A2 show a planar probe for use with a load-pulledoscillator system. FIGS. 1B1 and 1B2 show a modification of the planarprobe of FIG. 1, wherein an impedance transformer is included. FIG. 1Cshows a further modification of the planar probe of FIG. 1, wherein acoupled line structure is used.

FIGS. 2A1 and 2A2 show a planar probe with a terminating element. FIG.2B1 shows a detail view of the attachment of a resistor terminatingelement in the probe of FIG. 2A. FIG. 2B2 shows a detail view of theattachment of a short-circuit terminating element in the probe of FIG.2A. FIG. 2B3 shows a detail view of the attachment of a capacitorterminating element in the probe of FIG. 2A. FIG. 2B4 shows a detailview of the attachment of an inductor terminating element in the probeof FIG. 2A. FIG. 2B5 shows a detail view of the attachment of a diodeterminating element in the probe of FIG. 2A.

FIG. 2C shows a detail view of the attachment of the probe of FIG. 2A toa coaxial connector.

FIG. 3A shows a planar probe wherein the conductive traces are overlaidwith a cover of a material which is different from the substrate.

FIG. 3B shows assembly of a planar probe with a cover.

FIG. 4A shows a planar probe with an added selective absorption layer,for chemically selective signal enhancement. FIGS. 4B1 and 4B2 show aplanar probe with beads affixed thereto, for chemically selective signalenhancement. FIG. 4C shows a planar probe with an added selectiveabsorption layer and a stabilizing overcoat.

FIG. 4D shows a planar probe with an added selective absorption layerthereon, and with a heater integrated on the same substrate.

FIGS. 4E1 and 4E2 show a planar probe with TWO transmission lines (onlyone of them overlain by an added selective absorption layer), and an RFswitch to select which of the two transmission lines will be active.

FIG. 5A shows a coaxial load-pull measurement chamber with a tapereddielectric sheath on the central conductor.

FIG. 5B shows a planar tapered probe.

FIG. 6 shows an example of mounting a planar probe to monitor theelectrical characteristics of a fluid stream or a vessel.

FIGS. 7A1 and 7A2 show two views of a first sample embodiment of a patchantenna, for coupling through a dielectric wall (or window) toelectrically monitor the contents of a vessel or process flow. FIGS. 7B1and 7B2 show two views of a second patch antenna embodiment, which alsocan be used for monitoring materials through a dielectric wall.

FIG. 8 shows an example of mounting a patch antenna, in a reflectiveconfiguration, to monitor the electrical characteristics of a fluidstream or a vessel.

FIG. 9 schematically shows the electrical configuration used in thepresently preferred embodiments of the inventions.

FIG. 10 schematically shows the configuration of a complete system forimplementing the disclosed inventions.

FIG. 11A shows actual measured results from monitoring moistureabsorption by alumina beads (from Alcoa™) affixed to a planar probe.FIG. 11B is an expanded plot of some key data points from the plot ofFIG. 11A.

FIG. 12 shows actual measured results from monitoring moistureabsorption by a low-density alumina disk affixed to a planar probe.

FIG. 13 shows actual measured results from monitoring microcrystallinechanges during setting of a cement slurry. Various time intervals wereused as indicated by the drawing.

FIG. 14A shows actual measured results from monitoring conformationalchanges (molecular expansion) of xanthan from thermal treatment, using abare planar probe, and FIG. 14B is an expanded plot of some key datapoints from the plot of FIG. 14A. FIG. 14C is a plot showing measurementof the concentration of xanthan in water. FIG. 14D shows actual measuredresults from monitoring conformational changes (molecular expansion) ofstarch from thermal treatment, using a bare planar probe, and FIG. 14Eis an expanded plot of some key data points from the plot of FIG. 14D.

FIG. 15A shows actual data from compositional measurement of a mixtureof water with animal protein and fat, using a tapered planar probe witha cover.

FIG. 15B shows actual measured results from measurement of molecularmodification of protein (thermally) (i.e. cooking), using a planar probewith a sheath cover, and FIG. 15C is an expanded plot of some key datapoints from the plot of FIG. 15B.

FIG. 16A shows a family of curves from measurement of glucoseconcentration in a 0.1% saline solution, and FIG. 16B is a breakout ofdatapoints from the family of curves of FIG. 16A.

FIG. 17A shows a biomass determination, in which the presence of liveyeast is readily distinguished from the presence of dead yeast, and FIG.17B is an expanded plot of some key data points from the plot of FIG.17A.

FIG. 18A shows actual measured results from monitoring a fermentationprocess, using a planar probe, and FIG. 18B is an expanded plot of somekey data points from the plot of FIG. 18A.

FIG. 19A shows actual data from in-situ monitoring of enzymaticconversion of glucose to a glucose/fructose mixture, using a planarprobe, and FIG. 19B is an expanded plot of some key data points from theplot of FIG. 19A.

FIG. 20 shows actual data from in-situ monitoring of selectiveabsorption of glucose from a protein/saline solution onto a modifiedzeolite, using a planar probe (as shown in FIG. 4C) with an addedselected absorption layer and a stabilizing overcoat.

FIG. 21 shows actual data from in-situ monitoring of selectiveabsorption of ammonia from atmosphere performed at room temperatureusing a modified zeolite on a planar probe.

FIG. 22A shows a pair of sample curves of f_(osc) versus V_(tun), for asystem which has been modified, and FIG. 22B shows the differencebetween the derived data parameters corresponding to these curves. FIG.22C shows another pair of sample curves of f_(osc) versus V_(tun), for ahighly lossy composition before and after modification, and FIG. 22Dshows the difference between the derived data parameters correspondingto these curves.

FIG. 23 shows measurement of aging of a fat/protein mixture at ambienttemperature.

FIG. 24A shows a flow chart for process control based on a "processindex" value, derived as in FIGS. 22A-22D, in a simple process exampleas shown in FIG. 24B.

FIG. 25A shows a sample process flow for fermentation monitoringaccording to the disclosed inventions, and FIG. 25B shows a flow chartfor corresponding control logic, in which the capability of FIG. 25A isused for endpoint detection and yeast viability assurance. FIG. 25Cshows a fermentation process for sugar conversion, and FIG. 25D shows anenzymatic modification process.

FIG. 26A shows a sample setup for monitoring of material curingaccording to the disclosed inventions, and FIG. 26B shows a flow chartfor corresponding control logic, in which the capability of FIG. 26A isused for control of curing rate and also for endpoint detection.

FIG. 27A shows a simple process flow for monitoring of food processingaccording to the disclosed inventions, and FIG. 26B shows a flow chartfor corresponding control logic.

FIG. 28 shows an example of a Rieke plot, in which oscillator power andfrequency are plotted as a function of the load admittance presented atsome point in the output circuit of the oscillator.

FIGS. 29A-29C show three system configurations in which the disclosedinventions are used for humidity measurement.

FIG. 30 shows absorption/desorption cycling, for use of a probe having aselective absorption material and also a desorption heater.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

The numerous innovative teachings of the present application will bedescribed with particular reference to the presently preferredembodiment. However, it should be understood that this class ofembodiments provides only a few examples of the many advantageous usesof the innovative teachings herein. In general, statements made in thespecification of the present application do not necessarily delimit anyof the various claimed inventions. Moreover, some statements may applyto some inventive features but not to others.

Measurement System

FIG. 10 schematically shows the configuration of a complete system forimplementing the disclosed inventions. The chemical system undermeasurement interacts with the active planar probe 10 and produces ashift in the frequency of operation of the load pull oscillator 30. Thefrequency counter portion of the support electronics 40 accepts theoscillator's output, counts the number of zero crossings during a fixedtime interval, and provides the information to the signal processingsection. The frequency of the oscillator 30 is computed by theprocessing section. This frequency is then used in a polynomialequation, subtracted from a fixed numerical value, to obtain a processvalue. The analog and digital I/O sections of electronics 40 can receivecommands from the processing section and output analog or digitalsignals based on this process value. The operator interface provides theoperator with the means to change the polynomial or fixed numericalvalue, to set alarms and relay closing values and to range the output.Data logging can be obtained through a digital interface for connectionto a PC.

Electrical Configuration

FIG. 9 schematically shows the electrical configuration used toimplement the oscillator in the presently preferred embodiments of theinventions. The load seen at line RFOUT (presented by the measurementsection 800) is connected to the collector of driver transistor 910,while the tank circuit 34 is connected into the emitter-base coupling ofdriver transistor 910. The directional coupler 48 is a dual directionalcoupler which is connected directly to the line RFOUT.

Note that a small series resistor 912 is used in the RFOUT line. (In thepresently preferred embodiment, the value of this component is 9Ω.) Thisresistor helps to prevent spectral breakup (by suppressing oscillationat secondary frequencies).

A shunt resistor 914 is also attached to the RFOUT line. This resistoralso adds to stability, by fixing a maximum magnitude for the impedanceseen at line RFOUT. (In the presently preferred embodiment, the value ofthis component is 562Ω.)

These two resistors will reduce the magnitude of the frequency hopsseen, as discussed above.

The directional coupler preferably diverts only 1% of the reflectedpower, so that the load is still coupled closely enough to be able topull the oscillator. The corresponding output from coupler 48 isconnected to a frequency counter and control logic, as described above.Also, the two outputs from the directional coupler are used to measureinserted power and reflected power.

Planar Probes

The present application discloses a planar probe which can be readilyinserted into a variety of materials in solid, liquid, gas or plasmaphase. This probe provides a "single-ended" coupling element whichpermits load-pull measurements to be made on an increased variety ofmaterials. As with the coaxial configuration, oscillator frequency canbe monitored directly, or in combination with insertion loss.

FIGS. 1A1 abd 1A2 shows a planar probe for use with a load-pulledoscillator system. This probe contains a simple stripline structure,with a central strip 21 coupled to the central wire 22 of the coaxialinput, and a surrounding plane coupled to the shielding of the coaxialinput. This provides a simple constant-impedance transmission linestructure.

In a sample embodiment, the central strip 21 is 0.08" wide, and it isseparated from the adjacent plane 23 on either edge by a 0.03" gap. Theoverall dimensions of the substrate 24 are 0.75" by 2.375", and thestrip 21 is about 2" long. However, of course, these numbers are merelyillustrative, and can be readily varied. As will be recognized bymicrowave engineers, the dimensions should be selected to maintain animpedance match to the incoming line (which is a standard 50Ω coax, inthe presently preferred embodiment). This small structure permits readyinsertion into fluid streams; FIG. 6 shows an example of mounting aplanar probe 10 (like probe 11 of FIG. 1, or modified as describedbelow) on a standard flange for easy insertion into a process stream100. In some applications, it may be advantageous to position the probe10 so that its ground plane occupies the portions of the sensor whichmight be exposed to interferences to measurement, such as particles orgas bubbles.

A standard coaxial connector 25 is used, in the presently preferredembodiment, but of course other connectors can be used (or a coaxialline can be soldered directly to the probe). FIG. 2C shows a detail viewof the attachment of the probe of FIG. 2A to a coaxial connector, in asample preferred embodiment.

The transmission line does not necessarily have to end in an open, as inthe embodiment of FIG. 1A. Termination of this transmission line can beaccomplished in several ways. FIG. 2A shows a planar probe 12 with aterminating element 26. The chip termination 26 can be a resistor,capacitor, inductor, short, or diode. FIG. 2B1 shows a detail view ofthe attachment of a resistor terminating element 26A in the probe ofFIG. 2A. FIG. 2B2 shows a detail view of a short-circuit termination 26Bin the probe of FIG. 2A. FIG. 2B3 shows a detail view of the attachmentof a capacitor terminating element 26C in the probe of FIG. 2A. FIG. 2B4shows a detail view of the attachment of an inductor terminating element26D in the probe of FIG. 2A. FIG. 2B5 shows a detail view of theattachment of a diode terminating element 26E in the probe of FIG. 2A.

Selection of one of these terminations can be made in accordance withthe needs for measurement of particular materials. The resistivetermination could encompass from a short to an open depending upon thematerial under study and its reflections. If a magnetic material isunder study, it may be advantageous to have a short at the end orpossibly an inductive structure 26D. A pure dielectric would most likelybe optimum with an open or capacitive load to achieve a voltage maximumat the end of the probe. Other materials may be absorptive and respondbetter with a different impedance load than an open or short. A diodeload 26E could provide alternating capacitive/resistive loads each 1/2cycle in addition to providing a DC value relative to the power seen atthe load (the transmitted power as opposed to the reflected power). ThisDC value could be measured back at the oscillator end of the probe usingappropriate DC blocks and RF chokes to direct the DC voltage to avoltmeter.

Choice of Probe Substrate and Cover

The simplest substrate 24 is simply fired high-density alumina(essentially Al₂ O₃). This is commercially available, and is commonlyused for microwave circuits (due to its desirable low-loss properties).

Where environmental passivation is needed, and a slight degree ofdecoupling from the material under test is acceptable, a cover of firedhigh-density alumina can simply be epoxied onto the substrate andconductors.

Such high-density alumina is impermeable and inert. However, forhumidity-sensing applications, it may be preferable to use low-densitymaterial instead. Low-density alumina is somewhat porous, and has anaffinity for moisture, but still has reasonable mechanical properties.Thus a substrate and/or cover of low-density material can provide anenhanced signal for detection of ambient humidity changes.

Thus, one alternative is isostatic pressing a powdered compositematerial atop the substrate 24 and probe traces 21/23, and then bakingit to form a cover. The powdered composite material can optionally beadmixed with zeolites or other selective-absorbing material. FIG. 3Ashows a planar probe wherein the conductive traces 21/23 are overlaidwith a cover 27 of a material which is different from the substrate.Note also that an epoxy fill 22A is used to protect the connection ofcentral wire 22 to strip 21.

In a variation of this, the initial substrate 24 can also be made ofisostatic pressed low-density material, so that, after baking, thetraces are embedded in a solid body of absorbing material.

Alternatively, the cover 27 can be made of other materials such aslow-density alumina, fired alumina, other ceramic materials, or evenfiberglass.

The probe 10 can be used "bare", i.e. with the leads exposed, ifsufficiently inert metallization is used, e.g. gold or aself-passivating metallization such as stainless steel. Alternatively, athin applied passivation layer can be used, such as plasma-depositedperfluorocarbon.

The metallization 21/23, in the presently preferred embodiment, ismerely copper (since this can be processed easily with standardprinted-wiring-board processes). However, of course, numerous othermetallization materials and techniques can be used instead.

For materials having high ionic conductivity (and hence high RFabsorption), the conductors can be covered by a separate thin substrate.This would provide a propagation similar to a strip line mode where theupper and lower ground planes are in effect the conductive liquid undermeasurement.

However, in alternative embodiments (as discussed below), substrateswith other selective absorption properties can be used instead.

Adaptations of Probe Structure

Dielectric properties of particular fluids being measured can be allowedfor by alterations to the structures on the planar probe. This willprovide for better field patterns entering the fluids and therefore,increase the sensitivity to the variable under study.

One embodiment is the use of an aluminum oxide ceramic cover 27 over theconducting metallization for obtaining a better match into solutionscontaining ionic salts. The thickness of this ceramic substrate coveringwill impact the field patterns. Thinner covers would aid in heavy saltsolutions. The metallization can also be altered to achieve greaterfield strengths into the ceramic covers, and therefore into the fluids.These changes would be in the separation between the center conductorand the ground planes.

Other dielectric sandwiches can provide coupling to the medium understudy. The top side cover 27 can be of a high dielectric material whilethe substrate 24 on the lower side is made of a low dielectric. Thiswould help in measurements where the medium has vast changes indielectric constant.

FIGS. 1B1 and 1B2 show a modification of the planar probe of FIG. 1,wherein an impedance transformer is included. While this is not part ofthe presently preferred embodiment, it may be useful in matching to somematerials.

FIG. 1C shows a further modification of the planar probe of FIG. 1,wherein a coupled line structure is used. The additional lines 21Bprovide increased apparent line length, as well as some impedancetransformation. (Of course, proper selection of the cover and/orsubstrate material can also be used for adaptations to load density andpermittivity, as discussed above.)

The metallization may also be configured to achieve a spiral inductivepattern which would create specific magnetic field patterns to achieve apermeability measurement emphasis. This can optionally be combined withcoverings with magnetic characteristics to direct or concentrate themagnetic field.

The preferred embodiment uses various stripline configurations, butalternatively a slotline or other configuration can be used instead.

Probe with Extended Impedance Transformation

The present application discloses a probe which can be readily insertedinto a variety of materials in solid, liquid, gas or plasma phase. Thisprobe provides a "single-ended" coupling element which permits load-pullmeasurements to be made on an increased variety of materials.

A basic requirement of many applications is the need for measurement ofmaterials having a wide range of dielectric constant (ε from 1 to 180)using a single transmission line section. This may create problems inlaunching the electromagnetic energy into a different dielectric medium.Without some help in making a graceful transition from one propagationmedium to another (at a very different dielectric constant), the energywill simply be reflected.

The present disclosure teaches that a single-ended probe using a gradedimpedance (achieved by a planar tapered line or otherwise) can beparticularly advantageous for coupling a load-pulled oscillator to amaterial system to be monitored. In alternate embodiments, such probescan also be used for RF sensing in other electrical configurations,using standard instrumentation in the microwave industry as a part ofmaterial characterization problems. Such embodiments are lesspreferable, but can still confer some of the advantages of the claimedinventions.

It should also be noted that it may be advantageous to make the physicallength of a tapered probe longer than that of a corresponding straightprobe.

The preferred approach to this is a "tapered planar" structure, i.e. aplanar probe with a taper imposed on the trace geometries. An example ofthis is shown in FIG. 5B. This provides a compact single-ended probewhich can be used for load-pull or other characterization of widelyvarying material streams. The tapered central structure performs anextended impedance transformation across a significant distance whileelectromagnetically coupled to the material under test. This solves theproblem of coupling to the dielectric material. It also helps to solvethe problems of lossy materials (such as salt water), where thelossiness of the material can make it difficult to obtain any usablesignal at all.

FIG. 5A shows an alternative single-ended probe embodiment, for use withflow-through piping designs like those described in U.S. Pat. No.5,025,222, and PCT application WO 91/08469, both cited above. FIG. 5Ashows a load-pull measurement chamber 800' with a tapered dielectricsheath 810 on the central conductor 820. The extension of the basecenter rod 820 through the tapered sheath 810 provides for theelectrical length to increase with small ε_(n) since the lower ε_(n)will still be of sufficient impedance to allow the continual propagationof the electromagnetic wave. In the configuration shown, the top port802 is used for introduction of a temperature probe, and the processfluid flows from port 804 through to output port 806. It may be seenthat clearances are tight, in the configuration shown. The sheath 810 ispreferably machined with a flat (not shown) on its top side, for reducedflow resistance.

For lossy materials, the taper will also give a gradual entry into thehighly ionic fluids which should give rise to a graceful loss/lengthrelationship. For less lossy, low ε_(n) materials the bare rod shouldaid in the determination of the loss since it will more readily show lowloss.

If fluids with well known ε's are placed in this test section andfrequency and incident and reflected plowers noted, a calibration curveshould be generated which can be related to various VCO/pipeconfigurations. The pipe section used was a version of the 0.5" 5" longunit with 1/8" rod. The taper was across approximately 3" with thecenter rod protruding ≈1" past the end of the taper.

Probe with Selective Absorption Material

The present application discloses structures and methods for enhanced RFdetection using chemically selective materials on an RF probe. Thechemically selective material may be a coating, or may be part of thesubstrate, or may be a separate cover. At least part of the selectivematerial is placed in proximity to the RF propagation structure, so thatabsorption of a target species by the selective material will change thedielectric loading seen by the RF propagation structure.

The selective material can be attached in various ways. FIG. 4A shows aplanar probe 14 with an added selective absorption layer 28, forchemically selective signal enhancement. Note that, in the configurationof this Figure, the absorber ("active material") 28 overlies the cover27, as opposed to the more common configuration where the activematerial 28 substitutes for the cover 27.

FIG. 4B shows a planar probe 15 with beads 28" affixed thereto, forchemically selective signal enhancement.

FIG. 4C shows a planar probe 16 with an added selective absorption layer28 and a stabilizing overcoat (protective membrane) 28'. FIG. 3B showsassembly of a planar probe substrate 24 to a selective absorption layer28 and a stabilizing overcoat (protective membrane) 28'.

The selective material can be anything which will support anelectromagnetic field and have specific properties for a chemicalstructure. Examples include zeolites, ceramics with specificabsorptions, doped semiconductors which increase/decrease theirconductivity/dielectric constant with absorption. A further alternativeis the use of enzymes embedded in a porous structure which are alteredby selective substances may also be possible. This change in the enzymestructure would be visible with the load pull scheme. If a substrate wasembedded or coated with a material which would deteriorate withselective absorption, the monitoring of the degradation can give rise todetermination of the amount of the chemical present.

For another example, zirconia has unusual properties with oxygen at hightemperatures. It forms a ion exchange with oxygen molecules which isused to measure oxygen content of gas streams especially in cars andstack emission monitoring. It is contemplated that use of this as asubstrate can be advantageous for O₂ monitoring.

In the medical, food and pharmaceutical industries, it can beadvantageous to implement the selective-absorber substrate 16 as athrowaway substrate, to preserve sterility.

A particular advantage of the absorber-coated probe is that it can bedesigned to be self-calibrating. By contrast, other probes may need tobe calibrated with a sample which is (or approximates) the material inquestion.

FIG. 21 shows actual data from in-situ monitoring of selectiveabsorption of ammonia from atmosphere performed at room temperatureusing a modified zeolite on a planar probe. The absorbing element is amodified zeolite which absorbs NH₃ but not water. The initial oscillatorfrequency was about 1114.5 MHz, and this did not shift significantlywhile a flow of H₂ O-saturated nitrogen was applied. After an additionalflow of ammonia was added to the H₂ O-saturated nitrogen flow, theoscillator frequency shifted over a period of 30 minutes, as indicatedon the chart, by 4.8 MHz downward. (The numerals on the X-axis arearbitrary designators; each numeral corresponds to about 13 seconds.)Note that the rate of change declines markedly near the end, as theabsorber nears equilibrium with the vapor-phase concentration. Thespecific zeolite used in this experiment also selectively absorbs HCN,so this same structure can also be used for a danger warning in anenvironment, e.g. in metal-plating operations.

The simplest application of selective absorption is for humiditysensing, e.g. using an absorber of low-density Al₂ O₃ (alumina). Aluminawill equilibrate to a moisture concentration which is exactlyproportional (within a certain range) to the ambient humidity. (Theinteraction between alumina and water is typical of many materialssystems, where the relative equilibrium concentrations of a solute S inmaterials A and B are linearly related by a segregation coefficientk=[S]_(A) /[S]_(B).) However, the present invention does not require asmuch time as would be needed for equilibration. Instead, the rate ofuptake of humidity by the absorber is differentially monitored, and thisprovides a fast measurement which also is related to the ambienthumidity.

FIG. 11A shows actual measured results from monitoring moistureabsorption by alumina beads 28" (from Alcoa™) affixed to a planar probe15. In this Figure the oscillator frequency goes from 1230 to 1332 MHzas the tuning voltage is ramped from 4.3V to 20V. (In all of thefollowing plots of oscillator frequency versus tuning voltage, thetuning voltage is typically swept across the range shown in tens ofmilliseconds to tens of seconds.) FIG. 11B is an expanded plot of somekey data points from the plot of FIG. 11A. The top curve shows aninitial state, in which the oscillator frequency goes from about 1286 to1312.4 MHz as the tuning voltage is ramped from 7V to 13V. The arrowmarked * shows the shift in frequency behavior for 5 minutes exposure to100% relative humidity. In the resulting curve (the lowest shown), theoscillator frequency goes from below 1280 MHz to about 1306.5 MHz as thetuning voltage is ramped from 7V to 13V. The arrow marked ** shows thefurther shift in frequency behavior after exposure for 2 minutes to adry nitrogen flush. In this curve the oscillator frequency goes from1280 MHz to about 1307.6 MHz as the tuning voltage is ramped from 7V to13V.

FIG. 12 shows actual measured results from monitoring moistureabsorption by a low-density alumina disk affixed to a planar probe. Thisdisk was custom-made for this experiment by low-temperature sintering of"A-300" rehydratable activated alumina powder from LaRoche ChemicalsInc. Baton Rouge, La. Two parts of unground powder are mixed with onepart of water, pressed to shape, and baked for three hours at 400° C.

The multiple traces in FIG. 12 indicate successive runs at separatetimes t₁ -t₃. The last run (t₃) was made after 12 hours in approximately100% relative humidity. In this curve the oscillator frequency goes fromabout 1302 MHz to about 1317.1 MHz as the tuning voltage is ramped from10.1V to 20V. Also shown, for comparison, is a "0" line (0% humidity,desiccated) and a curve for the bare planar probe. In the "0" line curvethe oscillator frequency goes from about 1302.7 MHz to about 1320.4 MHzas the tuning voltage is ramped from 10.1V to 20V. Note that a frequencydifference of more than 3 MHz is seen at the highest frequency. Thus, byinterpolation, the minimum detectable humidity change would be about0.001%!

Note that the absorbent material need not be readily reversible. Forexample, there is a vast literature on customizing zeolite structures tomake "molecular sieves." However, the affinity of many such structuresfor their complementary substance is so high that the adsorbate is verytightly bound. Thus, a zeolite absorber may need to be periodicallypurged, or simply discarded when saturated.

FIGS. 29A-29C show three system configurations in which the disclosedinventions are used for humidity measurement. FIG. 29A shows a blower102 passing air over a humidifier 104, which is controlled in accordancewith measurements taken at the probe 10.

FIG. 29B shows a system configuration used to measure the moistureequilibrium of water vapor (and hence grain water content) in a grainstorage facility where air is flowed through a grain bin 106 to anexhaust port 108.

FIG. 29C shows a system configuration for measuring water content in anatural gas flow using RF probes 10, and controlling an ethylene glycoldryer column 107 accordingly.

One alternative class of embodiments uses an absorptive probe in asealed package: if an active matrix material such as a zeolite is usedfor moisture measurement in grains and food solids, a "zip open" sealedbag can be useful for field use.

For example, an RF probe with a dry active zeolite is shipped sealed ina plastic bag. When the customer is ready to actually make the fieldmeasurement, the probe is connected to the RF line and placed in acontainer (for example, a carload of grain), and the rip cord is pulledto open the bag and "activate the probe". This would allow use of azeolite material which is very aggressive (to water). The advantagewould be time to equilibrium. This may also be useful in other reactivesubstrate cases.

It should also be noted that the "absorber" material does not have to bea merely physical absorption, but may alternatively be a reactivematerial which chemically reacts (reversibly or irreversibly) with thetarget species.

Probe with Heater

A further embodiment provides an RF probe 17 which not only includes aselective-absorbing material 28 (such as alumina), but also includes aheater 29 for causing desorption of the absorbed material. This permitsthe heater to be "cycled" efficiently.

The heater 29 can be embedded in the ground plane or placed on thebackside of the substrate. This heater would be activated at either aset value of frequency change or at time intervals. During the on cyclethe change in the material can be simultaneously monitored by the sameload pulled oscillator to determine when the regeneration point has beenreached or to indicate to an operator that the time to replace the probeand material has arrived.

This embodiment also permits some aggressive absorbing materials (suchas high-affinity zeolites) to be used for selective absorption.

This embodiment is particularly attractive for field measurement ofhumidity, but can also be used for measurement of other substances.

In some applications, this heater can also be used to providetemperature regulation of the probe's immediate environment, if thematerial under test would not provide a heavy thermal load. For example,this may be useful where the sample is gaseous and of variabletemperature.

In the presently preferred embodiment of this invention, as shown inFIG. 4D, separate leads are provided to power two resistive heaters 29in a planar structure. However, in an alternative embodiment a resistiveheater can be driven by a DC component on the coaxial line (if the powerdetection diode is not used). In this embodiment, an isolatinginductance can be used with the heater to avoid resonances.

In a further alternative embodiment, a backside heater is combined witha ground plane. In this case the ground plane should preferably have areasonably high conductivity, to avoid excessive damping of the signalof interest, and therefore a low-voltage power supply is preferably usedfor the heater.

FIG. 30 shows absorption/desorption cycling, using a probe having aselective absorption material and also a desorption heater. Theselective absorption material, in this example, is selective to ammonia(NH₃). An air stream 110 with traces of ammonia is passed over an RFprobe 10 which includes a selective absorption element, and the changein oscillator frequency is used to monitor uptake of ammonia. When theabsorber becomes loaded, the heater is activated, and a new cycle ofabsorption is begun.) During each absorption cycle, the rate of uptakecan be measured using time-differentiated measurements. An integral isaccumulated to provide an index of the total loading of the absorber.The relation between this integral and the rate of uptake provides anindex of the ambient concentration. When the integral exceeds a certainthreshold, this indicates that the absorber is becoming fully loaded.The heater is then activated to refresh the absorber and start the cycleagain.

Probe with Two Selectable Transmission Lines

A further disclosed innovation is a single-ended probe which includesmultiple transmission line segments, and which also includes an RFswitching element connected to permit switching between the two segments(or at least controllable disabling of one segments). In the presentlypreferred embodiment, each transmission line is preferably nonresonantover the full range of frequencies of interest, although it may haveresonances at other frequencies. However, it is also contemplated, as analternative embodiment, that a structure which is resonant near a secondharmonic of the operating frequency may be advantageous.

FIG. 4E shows a planar probe 18 with TWO transmission lines 21D (onlyone of them overlain by an added selective absorption layer), and an RFswitch 22' to select which of the two transmission lines 21D will beactive.

There are many ways to use this capability. For example, one of the twolines can be an uncovered metal trace and the other can be covered witha material which selectively absorbs (or reacts with) a particularchemical. This combination would provide a measurement of a specificsubstance using the covered side of the probe, and once this componentof the material under study is known an additional component could bederived from the response from the bare side of the probe. For example,if the covered side uses an active material to discern glucose in adextrose/glucose/water mixture, the bare side's additional informationwould permit determination of the water content of the mixture.

This can also be used to provide spatially-resolved differentialmeasurement for detection of spatially-varying characteristics (e.g.material zone boundaries in a distillation or chromatographic column).

Patch Probe

In many applications the avoidance of direct contact with the materialsunder test is overwhelmingly desirable, to prevent contamination. Tomeet this need, the present application discloses a noninvasive RF probewhich can be readily coupled, through a dielectric window, to a materialunder test. This probe provides a "single-ended" isolated-couplingelement which permits load-pull measurements to be made on an increasedvariety of materials. The electrical configuration of this probe is likethat of a patch antenna, and hence this probe may be referred to as a"patch probe". The patch probe is inherently less sensitive than a probewhich is directly immersed in or inserted into the material under test,but may be sufficiently sensitive for many applications.

FIGS. 7A1 and 7A2 show a first sample embodiment 19A of a patch probe,for coupling through a dielectric wall (or window) to electricallymonitor the contents of a vessel or process flow. This embodiment uses aspiral-inductor configuration.

FIGS. 7B1 and 7B2 show two views of a second patch probe embodiment 19B,which also can be used for monitoring materials through a dielectricwall. In this embodiment the two leads of the incoming RF coaxial lineare connected to a center dot 19B2 and a peripheral ring 19B1, both madeof thick-film metallization. A circular patch 7B3, on the opposite sideof the dielectric puck, affects the near-field patterns to achieveproper electromagnetic coupling to the medium of interest.

FIG. 8 shows an example of mounting a patch probe, in a reflectiveconfiguration, to monitor the electrical characteristics of fluids 100in a pipe or vessel 110.

A planar probe can also be used for coupling through a window. In thiscase the planar probe would be placed flat against the window. However,the patch probe is preferred for such applications.

One alternative modification of the disclosed invention is to use a pairof probes as transmit and receive antennas for propagation of the RFenergy through a thickness of the material to be characterized. However,this is not presently preferred.

Method for Identifying Changes in a Given Process

The present application discloses a method for rapidly analyzing thestate of a given process. A load-pulled oscillator is coupled to thematerial under test, and is swept across a range of frequencies. Theoscillator frequency is swept, for example, by sweeping a tuningvoltage, applied to a varactor in the oscillator circuits, across apredetermined range. The oscillator is coupled to the material undertest by a probe which is electrically long (preferably at least severalhalf-wavelengths when fully loaded by the material under test). Thespecific conditions (probe type, physical conditions of coupling, andrange of tuning voltages or frequencies) will all have been previouslydefined, using the various considerations set forth in detail below. Theoscillator frequency is monitored while the tuning voltage is swept in apredetermined direction (up rather than down, for example).

For this defined set of conditions, each sweep of the tuning voltageV_(tun) will produce a corresponding range of oscillator frequencyvalues f_(osc). By integrating f_(osc) over the predetermined range ofV_(tun), a single derived index number results. This turns out to bevery useful in characterizing a given process under a given set ofconditions.

Part of the reason for this is that shifts in material composition whichproduce even very small shifts in permittivity will have the effect ofshifting the "knees" in the frequency curve. These knees, which arereadily visible in plots of oscillator frequency as a function of tuningvoltage, correspond to points where the oscillator phase goes through a180° transition. When this occurs, the oscillator will return to itsoriginal operating frequency, and this frequency is likely to shift.

To better explain this method, some more extensive analysis will now beprovided.

An oscillator builds up oscillations from a linear operating point if ithas more gain than is necessary for oscillations. The oscillations beginwith device noise as a triggering function. As the oscillations buildup, the gain is reduced due to the change in the operating point on theload line of the current/voltage relationships of the active device. Inessence, the device goes sufficiently far into saturation to reduce thegain to unity for the loop. This prevents the phase from being a simplelinear function of the load.

Now, consider what happens when load impedance varies.¹⁸ as the loadimpedance plane is traversed by the varying permittivity of the load,the gain and phase of the oscillator will shift in a non-linear fashionto maintain a unity gain and 180 degree phase shift. The point whichsatisfies both requirements of unity gain and 180 degree phase shift andthis point becomes the new frequency of operation. This is thephenomenon of "load pull," and is conventionally avoided by appropriateisolation of the oscillator from the load; but in the load-pulledoscillators used to implement the present inventions, of course it isnot desired to avoid this effect.

The load pull phenomena has a characteristic of a change in frequencywith a change in load impedance seen at the oscillator's outputterminal. However, this frequency cannot continue to changeindefinitely; it only changes up to a point where the phase exceeds 180degrees from the lowest frequency's impedance, and at this point theoscillator returns to its original frequency. These transitions will bereferred to herein as "knees."

Oscillator load pull is characterized by a graph called a Rieke plot. (Asample Rieke plot, for an ideal case, is attached as FIG. 28.) This is aplot of the oscillator power and frequency as a function of the loadadmittance¹⁹ presented at some point in the output circuit of theoscillator. It is presented on a Smith admittance chart with an overlayof constant power and frequency contours. The susceptance²⁰ component ofthe load admittance adds to the susceptance of the oscillator tankcircuit, to produce a net susceptance (or reactance) which determinesthe frequency of operation. The oscillator's susceptance must compensatefor this change in output admittance by a change in frequency to againcancel contribution from the output and meet the requirement for 180degrees of phase shift around the active device. The reason for this isbecause we are dealing with a transmission line system where the linelengths internal to the oscillator and the load can go from inductive tocapacitive at a given plane of reference at the output of theoscillator. (This explains the existence of "knees.") In addition, theoutput power relationships must also maintain a constant relationshipwith the conductance. In the purest case the lines of constantconductance relate directly to those of constant power, and those forconstant susceptance relate to constant frequency. Since this is thecase, the "Q" (resonant quality factor) of the oscillator's resonantcircuit determines the amount of frequency change per unit ofsusceptance. This "Q" factor is set by the circuit elements of theoscillator's feedback path. Deviations from this are seen in the actualRieke diagrams and are caused by the non-linear effects due to thechanges in device terminal susceptances as the device's operating pointgoes further into saturation (or out of saturation). Also, it can beshown that the output power is related to the load in such a fashionthat for increased output power, the unstable/no-oscillations regionabout the infinity portion of the Smith chart will increase in size.

Each unit change of susceptance can be related to the load impedances bythe equation for the reflection coefficient for a transmission line. Thevoltage reflection coefficient is ##EQU1## where Z_(o) is the standardimpedance of the 50-ohm coaxial line, and Z_(r) in this case is theinput impedance of the transmission line, or ##EQU2## where R, C, L, andG are distributed parameters for series resistance, shunt capacitance,series inductance, and shunt conductance, respectively. The reflectioncoefficient is the vector which describes the trajectory around theSmith chart which forms the outer bounds of the chart for an equalimpedance line of Z_(o). Since this equation relates the phase angle ofthe load to the impedance, the phase length (and therefore frequency)will become a function of the unit susceptance. Therefore, longertransmission lines will cross a given unit susceptance interval morequickly than shorter lines and increase the sensitivity of a load-pullsystem. This means that pulling is relational to the wavelength (whichis frequency and length).

In a typical application the oscillator's basic frequency can be forcedto change by the inclusion of a varactor (a voltage variable capacitor)in the primary resonant loop of the circuit. By applying a DC voltage onthis varactor, many oscillators can be tuned over an octave band. In thedescription above, the oscillator and load pull performance was assuminga fixed frequency (no varactor) circuit. If the load was a fixed lengthof lossless transmission line and the oscillator frequency was forced bythe applied voltage on the varactor as opposed to the load pullphenomena, the "knees" would be seen as the phase seen at the oscillatorwas swept through 180° because of the effect of decrease wavelengths athigher frequencies. The number of knees appearing in the voltage vsfrequency plot is dependent upon the dielectric constant of the mediumin the transmission line, the length of the line and the frequency.

FIG. 22A shows a pair of sample curves of f_(osc) versus V_(tun), for asystem which has been modified, and FIG. 22B shows the differencebetween the derived data parameters corresponding to these curves. Twosamples of gasoline with different water contents were measured. Anintegration of the area under the curve was done for both measurements,and the difference of the integrals was taken. The result is shown inthe FINAL RESULT plot. As more knees come into the plot, the integralincreases.

FIG. 22C shows another pair of sample curves of f_(osc) versus V_(tun),for a highly lossy composition (oil in 3% salt water) before and aftermodification, and FIG. 22D shows the difference between the derived dataparameters corresponding to these curves. The knees are not verydistinguishable because of the added loss is decreasing the sharpness ofthe 180 degree phase transitions. However, again the same trend is seenin the difference of the integrals for the two curves.

This technique can be used to eliminate the multiple valued problem thatmay exist if the oscillator is not a VCO (varactor controlledoscillator). As long as the process is slow enough to allow a sweep,exact values can be reproduced. If the process variable is changingduring a sweep the resultant data is an average value of the processduring that time interval. This provides for a graceful measurementunder any circumstances.

In an alternative class of embodiments, signal processing software isused to look at not only the frequency response, but also the time rateof change and a slope of the frequency as tuning voltage is swept at aconstant rate. Both of these factors can provide further differentiatedcharacterizations of both the materials and the baseline chemical. Thefrequency sweep can thus detect very slow polar moments (KHz variety)even though the system is operating at microwave frequencies. This mayespecially be true with some of these crystal like structures which willhave long relaxation times. It also would be indicative of the amount of"loading" of the planar substrate absorptive material at that particulartime.

In the experimental runs given herein, the tuning voltage V_(tun) istypically swept across the whole range shown every 100 milliseconds orso. However, by varying the rate of voltage sweep, phenomena havingdifferent relaxation time constants may be distinguished. See generallyMcCrum et al., ANELASTIC AND DIELECTRIC EFFECTS IN POLYMERIC SOLIDS(1967), which is hereby incorporated by reference. (In productioninstallations, it is generally preferable to simply let the oscillatorrun at a fixed frequency.)

Thus, simple data reduction can be performed to derive a single indexnumber for a given set of conditions. This is particularly useful wherea given system is being tracked over time, since the time-domainbehavior of the index number can easily be tracked. Thus, for instance,for endpoint detection in monitoring a batch process, the endpoint canbe identified when the index value has shifted by a certain percentagefrom its initial value and the rate of change has declined to a certainpercentage of its maximum value during the process run.

FIG. 24A shows a flow chart for process control based on a "processindex" value, derived as in FIGS. 22A-22D, in a simple process exampleas shown in FIG. 24B. In this example, flow of material 100 into thevessel 110 is controlled in real time by electronics 40', in accordancewith the above procedures, using a probe 10 and voltage-controlledoscillator 30.

Monitoring Fermentation Processes

The present application discloses processes for monitoring bulkfermentation, and for partially characterizing the composition of abatch fermentation, by observing the frequency of a load-pull oscillatorwhich is RF-coupled to the material under test (preferably by a simplesingle-ended RF probe).

Most pharmaceutical fermentations are done in a small batch mode wherethere is no flow. The planar probe structure is very well adapted tosuch applications. The planar structure also lends itself to throw awayreplacements to maintain sensitivities and prevent bacteriologicalgrowth in these sensitive vats. Of course, sterile load-lock proceduresare preferably used for insertion of a sterile RF probe into a culturevat.

It should be noted that the disclosed methods are not only useful forpharmaceutical applications, but may also be useful in brewing,winemaking, and in food industry processes using biologically activeagents.

The disclosed methods also permit the biomass of a fluid stream to bemeasured. Thus metering of a starter culture can be optimized withoutwaste.

The disclosed methods also provide a direct test for yeast viability insolution. Thus the presence of yeast activity can be checked during theearly stages of fermentation, before the yeast mass has multipliedsufficiently to be unmistakably active.

FIG. 25A shows a sample process flow for fermentation monitoringaccording to the disclosed inventions, and FIG. 25B shows a flow chartfor corresponding control logic, in which the capability of FIG. 25A isused for endpoint detection and yeast biomass control.

FIG. 25A shows a typical antibiotic production process. After thefermentation process has gone to completion (or at least begun to slowdown), the liquor from the vat 112 is passed to an extraction stage 116,for removal and purification of the desired end-product. For antibioticextraction, this may be, for example, a liquid-liquid extraction using amethyl acetate/heptane solvent. (Of course, the extraction andpurification operations can be very complex indeed, and the single stageshown is merely illustrative.)

Bio-mass measurement is performed on the organisms as they areintroduced into the fermentation tank 112 from the starter stock 114.This permits the amount of the starter culture (which otherwise has tobe measured by volume) to be optimized, avoiding unnecessary consumptionof the starter culture and also avoiding unnecessary delay in thefermentation process.

An initial measurement is taken on the loaded Fermentation tank 112 toproduce a "process signature". This is then used as a baseline to trackthe progress of fermentation. A load-pulled oscillator, connected to theprobe 10 at port 111, is then used to monitor progress of thefermentation, and to determine when to transfer the liquor to theextraction column.

In the embodiment shown, additional probe interfaces 10 are locatedbefore and after the extraction column 116, to provide a measure ofcolumn up-take efficiency. This permits the user to accurately optimizethe trade-off between efficient use of solvent and efficient extractionof product.

FIG. 25C shows a fermentation process for sugar conversion, and FIG. 25Dshows an enzymatic modification process. In this process glucoseIsomerase is used to convert into a glucose+fructose mixture ("HFSC").Control logic like that of FIG. 25B can be analogously applied, mutatismutandis, to these cases too.

FIG. 18A shows actual measured results from monitoring a fermentationprocess, using a planar probe. The trials of FIGS. 18A and B wereperformed with 500 ml H₂ O at 45° C., using 2.5 g dry yeast and 10 gfructose. The yeast used was standard dried baking yeast packaged forconsumer use. The yeast was initially started in a portion of the warmwater, and then all ingredients were combined. The curve marked "start"shows an initial measurement after mixing the yeast starter culture intothe nutrient solution. In this curve the oscillator frequency goes fromabout 1162 MHz to about 1182 MHz as the tuning voltage is ramped fromabout 3.5V to 6.6V. Fermentation was then performed for 12 hours. Thecurve marked "finish" shows another set of measurements which were thentaken. In this curve the oscillator frequency goes from about 1162 MHzto about 1218 MHz as the tuning voltage is ramped from 3.5V to 6.6V.

FIG. 18B is an expanded plot of data points from the plot of FIG. 18A ata constant V_(tun) =20V. (The numbers on the X-axis of this plot areinsignificant; this plot is merely a graphic way to indicate the largeobserved difference in oscillator frequency at a given tuning voltage.By dividing this observed frequency difference by the frequencyresolution of 30 Hz, it may be seen that the plotted difference is manytimes the least-measurable-increment.)

Applications of the Phase Transition Model to Intact Cells

It has been known for many years that when dry organisms such as yeastcells and seeds and pollen of plants are placed in cold water, they leaktheir contents into the water and are killed. (It has been reported thatthe reason for this effect has been reported to be identical to themechanism explained above for liposomes (32-34). Dry baker's yeast, forinstance, must be rehydrated above about 40° C. Below that temperature,the cells leak their contents during rehydration and are killed.However, if the dry cells are placed in water >40° C., their membranephospholipids undergo a phase transition during rehydration.

FIG. 17A shows a biomass determination, in which the presence of liveyeast is readily distinguished from the presence of dead yeast. In theexperimental setup, 5 grams of yeast was mixed with 200 ml of H₂ O toproduce a 2.4% solution (5/205). This was measured at 30° C. after yeastwas mixed in two runs at 4° C. and 45° C. (Mixture at 4° C. kills theyeast.) A measurement of pure water was also taken for comparison. At afixed tuning voltage of 20V, the oscillator frequency was 1280.93 MHzfor pure water, 1282.48 MHz for water with dead yeast, and 1285.4 MHzfor water with live yeast. FIG. 17B is an expanded plot of some key datapoints from the plot of FIG. 17A. The numbers on the X-axis of this plotare insignificant; this plot is merely a graphic way to indicate thelarge observed difference in oscillator frequency at a given tuningvoltage. By dividing this observed frequency difference by the frequencyresolution of 30 Hz, it may be seen that the plotted difference is about100,000 times the least-measurable-increment. Thus, it may be seen thatload-pulled measurement provides sensitive discrimination between equalconcentrations of live and dead yeast, and thus provides a technique fordirect measurement of biomass.

Monitoring Curing and Crystallization Processes

The present application discloses processes for monitoring the state ofcuring (or microcrystalline change) of solid materials, by observing thefrequency of a load-pull oscillator which is RF-coupled to the materialunder test (preferably by a simple single-ended RF probe).

One area where this technique is of particular interest is in monitoringthe curing of shaped aerodynamic composite materials.

FIG. 26A shows a sample setup for monitoring of material curingaccording to the disclosed inventions, and FIG. 26B shows a flow chartfor corresponding control logic, in which the capability of FIG. 26A isused for control of curing rate and also for endpoint detection. In thesetup of FIG. 26A, a gel 120 is preferably used to provide reliablecontact and good coupling between a single-ended probe (e.g. a patchprobe 19) and a formed body 122 of material undergoing cure.

Another area of particular interest is in monitoring the curing ofconcrete and cement compositions. Cement curing is a complex processwhich requires a fairly extended period. In curing Portland cement (andrelated compounds), it is generally desirable not to cure too rapidly.Dendritic crystallite growth occurs during the normal curing process,and the interpenetration and interlocking of the resulting crystallitesgives the final material its strength. If curing is performed toorapidly, this interpenetration will not occur, and the material will beweaker.

To meet this need, the present application also provides methods formonitoring and controlling the rate of cure of composite materials. Whenthe real-time monitoring process indicates that the rate of cure isexcessive, then steps are taken to reduce the rate of cure (normally bylowering the temperature).

Where it is required merely to detect the endpoint of a curing process,a useful alternative is to use rate-of-change measurements instead of(or in combination with) absolute measurement.

FIG. 13 shows actual measured results from monitoring microcrystallinechanges during setting of a cement slurry. Various time intervals wereused as indicated by the drawing. The curve marked "start" actuallyincludes multiple traces, taken at 30 second intervals; but at thispoint the shift in properties is sufficiently slow that the differenttraces cannot be separated by eye on the plot shown. In this curve theoscillator frequency goes from about 1127 MHz to about 1283 MHz as thetuning voltage is ramped from 2.2V to 13.2V. The second group of curves,taken at 5 minute intervals 30 minutes after beginning, shows someseparation of the individual traces at the higher tuning voltages. Inthis Figure the oscillator frequency goes from about 1120 MHz to about1262 MHz as the tuning voltage is ramped from 2.2V to 13.2V. (Note toothat a significant spread is seen among the 5-minute-separated runs atthe higher tuning voltages.) The last trace, taken 7 days later, showsthe markedly different properties of the solidified material. In thiscurve the oscillator frequency goes from about 1155 MHz to about 1192MHz as the tuning voltage is ramped from 2.2V to 13.2V.

Food Analysis and Food Process Monitoring

The present application discloses processes for monitoring the state ofprocessing of, and for partially characterizing the composition of, foodand feed products, by observing the frequency of a load-pull oscillatorwhich is RF-coupled to the material under test (preferably by a simplesingle-ended RF probe).

The simplest way to use this monitoring technique analytically is tolook at the time derivative of the measured RF frequencies: a certainpercentage decrease in the rate of change can be used for an endpointsignal, to terminate a batch cooking stage. (Of course, this percentagedecrease would be customized for a particular process, and would allowfor continued cooking as the temperature of the food materials is rampeddown.)

FIG. 27A shows a simple process flow for monitoring of food processingaccording to the disclosed inventions, and FIG. 27B shows a flow chartfor control logic corresponding to FIG. 27A. In this sample flow, animalparts are fed through grinder 132 and cooker 134 to evaporator 138. Thewater injector 136 is regulated, using measured data from the probe 10,to achieve a water content into the evaporator of 40 to 50%. (Too lowwater content will cause the evaporator to clog; too high a watercontent will waste energy in the evaporator.)

FIG. 14A shows actual measured results from monitoring conformationalchanges (molecular expansion) of xanthan from thermal treatment, using abare planar probe. The bottom curve shows uncooked material. In thisFigure the oscillator frequency goes from about 1233 MHz to about 1271.4MHz as the tuning voltage is ramped from 10V to 20V. In this curve theoscillator frequency goes from about 1233.4 MHz to about 1274.2 MHz asthe tuning voltage is ramped from 10V to 20V. FIG. 14B is an expandedplot of some key data points from the plot of FIG. 14A. (The numbers onthe X-axis of this plot are insignificant; this plot is merely a graphicway to indicate the large observed difference in oscillator frequency ata given tuning voltage. By dividing this observed frequency differenceby the frequency resolution of 30 Hz, it may be seen that the plotteddifference is many times the least-measurable-increment.)

FIG. 14C is a plot showing measurement of the concentration of xanthanin water. In this curve the oscillator frequency goes from about 620.55MHz to about 617.7 MHz as the concentration of xanthan is varied from 0%to 2.0%.

Xanthan is a polysaccharide which is in some ways analogous to starch.Similar measurements of starch under heat treatment have yielded curvessimilar to those of FIGS. 14A and 14B. FIG. 14D shows actual measuredresults from monitoring conformational changes (molecular expansion) ofstarch from thermal treatment, using a bare planar probe. In thisprocess a 7% solution of starch was heated for 20 minutes at 70° C. Themeasurement was performed at room temperature. The curve marked "before"shows starch which has not undergone the conformational changes inducedby heat treatment; in this curve the oscillator frequency goes fromabout 1240 MHz to about 1255 MHz as the tuning voltage is ramped from 8Vto 10V. The curve marked "after" shows starch which has been cooked. Inthis curve the oscillator frequency goes from about 1240 MHz to about1246 MHz as the tuning voltage is ramped from 8V to 10V. The bottomcurve is a measurement of reflected power, and shows the general shapeof an insertion loss measurement.

FIG. 14E is an expanded plot of some key data points from the plot ofFIG. 14D. (The numbers on the X-axis of this plot are insignificant;this plot is merely a graphic way to indicate the large observeddifference in oscillator frequency at a given tuning voltage. Bydividing this observed frequency difference by the frequency resolutionof 30 Hz, it may be seen that the plotted difference is many times theleast-measurable-increment.)

FIG. 15A shows actual data from compositional measurement of variousmixtures of water with animal protein and fat, using a tapered planarprobe with a cover. The top curve shows measurement of a mixture ofprotein alone (19% wt protein in water). In this curve the oscillatorfrequency goes from about 391 MHz to about 439 MHz as the tuning voltageis ramped from 13V to 20V. The middle curve shows measurement of anequal mixture of the protein solution of the first curve with chickenfat. In this curve the oscillator frequency goes from about 390 MHz toabout 430.5 MHz as the tuning voltage is ramped from 13V to 20V. Thebottom curve shows measurement of pure chicken fat. In this curve theoscillator frequency goes from about 391 MHz to about 400 MHz as thetuning voltage is ramped from 13V to 20V.

FIG. 15B shows actual measured results from measurement of molecularmodification of protein (thermally) (i.e. cooking), using a planar probewith a sheath cover. The top curve shows measurement of an uncookedslurry of animal protein in water. In this curve the oscillatorfrequency goes from about 1189 MHz to about 1281 MHz as the tuningvoltage is ramped from 6.6V to 19.8V. The bottom curve shows measurementof the same slurry composition after cooking. In this curve theoscillator frequency goes from about 1189 MHz to about 1274 MHz as thetuning voltage is ramped from 6.6V to 19.8V. FIG. 15C is an expandedplot of some key data points from the plot of FIG. 15B. (The numbers onthe X-axis of this plot are insignificant; this plot is merely a graphicway to indicate the large observed difference in oscillator frequency ata given tuning voltage. By dividing this observed frequency differenceby the frequency resolution of 30 Hz, it may be seen that the plotteddifference is many times the least-measurable-increment.)

It should be noted that such electrical measurement of cookingoperations is preferably used in combination with temperaturemonitoring. However, since many cooking operations are isothermal,temperature measurement cannot provide endpoint detection.Alternatively, a controlled time/temperature profile can be used, butthis too does not permit endpoint detection by measurement oftemperature.

FIG. 16A shows a family of curves from measurement of glucoseconcentration in a 0.1% saline solution. The measurements were performedwith a planar, bare, shorted probe configuration at room temperature. Inthe plot for a 2% solution, the oscillator frequency goes from about1202 MHz to about 1210 MHz as the tuning voltage is ramped from 6.6V to8.8V. Also plotted for comparison is a solution with no glucose present.In this curve the oscillator frequency goes from about 1163 MHz to about1178 MHz as the tuning voltage is ramped from 6.6V to 8.8V. (In general,the 0% point in "binary" plots of complex systems is usuallysignificantly separated from the other points, as in the example shown.This is usually caused by hydrolization or formation of other bonds.)The intermediate curves correspond to intermediate concentrations (1%and 0.5%) of glucose. FIG. 16B is a breakout of datapoints from thefamily of curves of FIG. 16A. (The numbers on the X-axis of this plotare insignificant; this plot is merely a graphic way to indicate thelarge observed difference in oscillator frequency at a given tuningvoltage. By dividing this observed frequency difference by the frequencyresolution of 30 Hz, it may be seen that the plotted difference is manytimes the least-measurable-increment.)

FIGS. 19A and 19B show measurement of the fructose percentage in a rangeof glucose/fructose mixtures, using a bare planar probe. FIG. 19A showsmeasurements at a constant tuning voltage of 15V. In this curve theoscillator frequency goes from about 1263.9 MHz to about 1261.8 MHz asthe concentration varies from 0% wt fructose to 54% wt fructose. FIG.19B shows measurements at a constant tuning voltage of 20V. In thiscurve the oscillator frequency goes from about 1277.3 MHz to about1275.3 MHz as the concentration varies from 0% wt fructose to 54% wtfructose. In all of these experimental measurements, the initial mixturewas 45% solids and 55% H₂ O by weight. This capability permitshigh-resolution in-situ real-time monitoring of enzymatic conversion ofglucose to a glucose/fructose mixture.

One of the common goals of food processing is to prepare sweetenedmaterial from grains, particularly corn (maize). The normal processingcycle uses a series of enzymatic and catalytic digestion steps in thesequence starch→dextrin→maltose→glucose+fructose. (Fructose is anattractive end-product, since it is much sweeter than glucose.)

FIG. 20 shows actual data from in-situ real-time monitoring of selectiveabsorption of glucose from a protein/saline solution onto a modifiedzeolite, using a planar probe (as shown in FIG. 4C) with an addedselective absorption layer and a stabilizing overcoat. The solutionconsists of 10% protein (emulsion), 0.1% NaCl saline solution, and 5%glucose solution all measured at room temperature. In this curve theoscillator frequency (at a constant tuning voltage of 10V) goes fromabout 1220.6 MHz to about 1218.3 MHz within about 10 minutes afterimmersion. At this time the absorber was apparently approachingequilibrium (or becoming loaded), since the rate of change of theoscillator frequency was markedly reduced. The final measured data pointshowed an oscillator frequency of about 1218.2 MHz after 15 minutes. Theprotein in this mixture shows that the selective absorption measurementworks well in the presence of other complex biomaterials. Thus, thisoperation may be used for monitoring simple materials (such as glucose)in very complex mixtures (such as food ingredients, or materials ofmedical interest such as blood or urine).

FIG. 23 shows aging of a fat/protein mixture at ambient temperature. Ablended mix of 1 part animal protein in 2 parts of water was allowed toage in an uncovered beaker for 16 hours at room temperature (about 25°C.). Thus, this system provides a proxy for deterioration ofprotein-rich food products due to oxidation, bacterial growth, etc.Time-resolved measurements were taken, without sweeping the oscillator(V_(tun) =12V), at two points 16 hours apart. During the 16 hours, theoscillator frequency changed from 1245.62 MHz to 1230.1 MHz, for achange of 15.52 MHz. The specified resolution of the frequencymeasurement apparatus used (shown in FIG. 10) is about 30 Hz. (Theactual resolution is significantly better--probably close to 10 Hz).Thus, the measured change is more than 500,000 times the minimummeasurable increment. The shape of the curve is typically an exponentialor power-law curve, but straight-line interpolation of the number ofdatapoints over the time interval corresponds to one detectableincrement every seven seconds! Thus, even assuming that the rate ofchange is much slower at first, the very high resolution provided by thedisclosed inventions permits accurate detection of the smaller rate ofchange at the beginning of the process.

Further Modifications and Variations

It will be recognized by those skilled in the art that the innovativeconcepts disclosed in the present application can be applied in a widevariety of contexts. Moreover, the preferred implementation can bemodified in a tremendous variety of ways. Accordingly, it should beunderstood that the modifications and variations suggested below andabove are merely illustrative. These examples may help to show some ofthe scope of the inventive concepts, but these examples do not nearlyexhaust the full scope of variations in the disclosed novel concepts.

For example, the preferred method of monitoring the characteristics ofthe material in the test loop is simply by observing the shifts in thefrequency of the free-running oscillator, as discussed above; but in analternative class of embodiments, the behavior of the free-runningoscillator may be observed in a different way: instead of monitoring thefrequency of oscillation, a phase-lock loop configuration can be used,and the error signal of the phase-lock loop tracked. This is essentiallyequivalent to observing the frequency shifts which would have occurredwithout the feedback control relationship used to implement thephase-locked-loop (or frequency-locked-loop) configuration.

In phase-locked-loop systems, a phase detector is used to detect phasedifferences between a reference signal and the output of avoltage-controlled oscillator. The phase-detector generates an errorsignal accordingly, which is usually combined with a control signal, andfed back to control the voltage-controlled oscillator. Thus, thevoltage-controlled oscillator very accurate tracks the reference signal,even if the frequency of reference signal varies. See Phase Locked Loops(Edited William Lindsey and Chak M. Chie, 1986); Floyd M. Gardner,Phaselock Techniques (2nd Ed., 1979); Roland E. Best, Phase-locked Loops(1984); D. Wolaver, Phaselocked Loop Circuit Design (1991); all of whichare hereby incorporated by reference. Of course, for high frequencysystems, as in some embodiments of the present invention, conversion isused before the phase detection operation. In addition, as detailed inthe foregoing references, higher-order phase-locked-loops with multiplestages of feedback can be used, and nonlinear relations can be added ifdesired.

Some background on microwave phase-locked loops may be found in thearticle by Zvi Galani and Richard Campbell, at 39 IEEE Transactions onMicrowave Theory and Techniques, 782 (May 1991), which is herebyincorporated by reference.

In modern telecommunications technology, analog phase-locked-loops havebeen very widely replaced by digital PLL's. In a digitalphase-locked-loop, the error signal is a numerical value, and thevoltage-controlled oscillator is instead a numerically-controlledoscillator. Discussion of such digital PLL circuits may be found, forexample, in W. C. Lindsey and C. M. Chie, "A survey of digitalphase-locked loops," 69 PROCEEDINGS OF THE IEEE 410ff (1981), and thecomments on that article published at 70 PROC. IEEE 201ff (1982).

As will be recognized by those skilled in the art, the innovativeconcepts described in the present application can be modified and variedover a tremendous range of applications, and accordingly the scope ofpatented subject matter is not limited by any of the specific exemplaryteachings given.

What is claimed is:
 1. A method for monitoring the state of curing ormicrocrystalline change of solid materials, comprising the stepsof:combining precursor components to provide a body having a desiredphysical shape; electromagnetically coupling a single-ended nonresonantRF probe to said body, and connecting said probe to an oscillatoroperating at more than 100 MHz, with no RF buffer stage being interposedbetween said oscillator and said probe; and observing time-dependentchanges in the frequency behavior of said oscillator, to detect changesin the composition or microcrystalline structure of said body.
 2. Amethod for controlling a process of curing a predetermined solidmaterial, comprising the steps of:combining precursor components toprovide a body of said predetermined solid material; electromagneticallycoupling a single-ended nonresonant RF probe to said body, andconnecting said probe to an oscillator operating at more than 100 MHz,with no RF buffer stage being interposed between said oscillator andsaid probe; and observing time-dependent changes in the frequencybehavior of said oscillator, to detect changes in the composition ormicrocrystalline structure of said body.
 3. The method of claim 2,wherein said RF probe is a single-ended probe including a section oftransmission line which is electromagnetically coupled to materials inproximity thereto.
 4. The method of claim 2, wherein said RF probe isinserted into said body.
 5. The method of claim 2, wherein said RF probeis not inserted into said body, but is placed in proximity therewith. 6.A method for processing food and analogous materials, comprising thesteps of:providing multiple process feeds of ingredient materials;electromagnetically coupling a single-ended nonresonant RF probe to atleast one said feed of ingredient materials, said probe beingelectrically connected to a free-running RF oscillator, with no RFbuffer stage being interposed between said oscillator and said probe;and observing the frequency behavior of said oscillator, to detectvariation in the composition of said respective feed of ingredientmaterials; and combining and processing said feeds of ingredientmaterials to provide a food product, while dynamically controlling oneor more process parameters in accordance with results of said observingstep.
 7. The method of claim 6, wherein said observing step monitorssaid materials for spoilage.
 8. The method of claim 6, wherein saidobserving step monitors said materials for fat content.
 9. The method ofclaim 6, wherein said observing step monitors said materials for sugarcontent.
 10. A method for cooking food and analogous materials,comprising the steps of:introducing a mixture of predeterminedingredients into a cooking vessel; applying heat to said vessel in acontrolled temperature-versus-time relationship, to cook said mixture;electromagnetically coupling a nonresonant RF probe to said mixture insaid vessel, and connecting said probe to an oscillator operating atmore than 100 MHz, with no RF buffer stage being interposed between saidoscillator and said probe; observing the frequency behavior of saidoscillator, to detect changes in the molecular composition or molecularexpansion of said mixture; and unloading said vessel at a time which isat least partially determined by the results of said observing step.